Update links in documentation to point at new example locations (#18931)

## Which issue does this PR close?

- part of #18142 

## Rationale for this change

@cj-zhukov has been consolidating the examples, but that also means that
the links to the examples are now out of date



## What changes are included in this PR?

Update links (I used openai codex, with the prompt below) and reviewed
the results

<details><summary>Prompt</summary>
<p>

```
We have moved the examples around in datafusion-examples/

  There are some links in doc comments such as in `datafusion/src/lib.rs`:

  [`expr_api`.rs]: https://github.com/apache/datafusion/blob/main/datafusion-examples/
  examples/expr_api.rs

  This example has been moved to ./datafusion-examples/examples/query_planning/
  expr_api.rs

  Please look for all other links to datafusion-examples and update them if necessary to
  point at the new path.
```

</p>
</details> 

## Are these changes tested?

By CI
## Are there any user-facing changes?

Fixed docs

Author: alamb

datafusion/core/src/execution/context/mod.rs

@@ -785,7 +785,7 @@ impl SessionContext {
     /// * [`SessionState::create_physical_expr`] for a lower level API
     ///
     /// [simplified]: datafusion_optimizer::simplify_expressions
-    /// [expr_api]: https://github.com/apache/datafusion/blob/main/datafusion-examples/examples/expr_api.rs
+    /// [expr_api]: https://github.com/apache/datafusion/blob/main/datafusion-examples/examples/query_planning/expr_api.rs
     pub fn create_physical_expr(
         &self,
         expr: Expr,
@@ -1903,7 +1903,7 @@ pub trait QueryPlanner: Debug {
 /// because the implementation and requirements vary widely. Please see
 /// [function_factory example] for a reference implementation.
 ///
-/// [function_factory example]: https://github.com/apache/datafusion/blob/main/datafusion-examples/examples/function_factory.rs
+/// [function_factory example]: https://github.com/apache/datafusion/blob/main/datafusion-examples/examples/builtin_functions/function_factory.rs
 ///
 /// # Examples of syntax that can be supported
 ///

datafusion/core/src/execution/session_state.rs

@@ -707,7 +707,7 @@ impl SessionState {
     /// * [`create_physical_expr`] for a lower-level API
     ///
     /// [simplified]: datafusion_optimizer::simplify_expressions
-    /// [expr_api]: https://github.com/apache/datafusion/blob/main/datafusion-examples/examples/expr_api.rs
+    /// [expr_api]: https://github.com/apache/datafusion/blob/main/datafusion-examples/examples/query_planning/expr_api.rs
     /// [`SessionContext::create_physical_expr`]: crate::execution::context::SessionContext::create_physical_expr
     pub fn create_physical_expr(
         &self,

datafusion/core/src/lib.rs

@@ -360,7 +360,7 @@
 //! [`TreeNode`]: datafusion_common::tree_node::TreeNode
 //! [`tree_node module`]: datafusion_expr::logical_plan::tree_node
 //! [`ExprSimplifier`]: crate::optimizer::simplify_expressions::ExprSimplifier
-//! [`expr_api`.rs]: https://github.com/apache/datafusion/blob/main/datafusion-examples/examples/expr_api.rs
+//! [`expr_api`.rs]: https://github.com/apache/datafusion/blob/main/datafusion-examples/examples/query_planning/expr_api.rs
 //!
 //! ### Physical Plans
 //!
@@ -649,7 +649,7 @@
 //!
 //! [Tokio]:  https://tokio.rs
 //! [`Runtime`]: tokio::runtime::Runtime
-//! [thread_pools example]: https://github.com/apache/datafusion/tree/main/datafusion-examples/examples/thread_pools.rs
+//! [thread_pools example]: https://github.com/apache/datafusion/blob/main/datafusion-examples/examples/query_planning/thread_pools.rs
 //! [`task`]: tokio::task
 //! [Using Rustlang’s Async Tokio Runtime for CPU-Bound Tasks]: https://thenewstack.io/using-rustlangs-async-tokio-runtime-for-cpu-bound-tasks/
 //! [`RepartitionExec`]: physical_plan::repartition::RepartitionExec

datafusion/datasource-parquet/src/source.rs

@@ -240,7 +240,7 @@ use parquet::encryption::decrypt::FileDecryptionProperties;
 ///
 /// For a complete example, see the [`advanced_parquet_index` example]).
 ///
-/// [`parquet_index_advanced` example]: https://github.com/apache/datafusion/blob/main/datafusion-examples/examples/advanced_parquet_index.rs
+/// [`parquet_index_advanced` example]: https://github.com/apache/datafusion/blob/main/datafusion-examples/examples/data_io/parquet_advanced_index.rs
 ///
 /// # Execution Overview
 ///

datafusion/execution/src/memory_pool/pool.rs

@@ -319,8 +319,8 @@ impl TrackedConsumer {
 ///
 /// For more examples of using `TrackConsumersPool`, see the [memory_pool_tracking.rs] example
 ///
-/// [memory_pool_tracking.rs]: https://github.com/apache/datafusion/blob/main/datafusion-examples/examples/memory_pool_tracking.rs
-/// [memory_pool_execution_plan.rs]: https://github.com/apache/datafusion/blob/main/datafusion-examples/examples/memory_pool_execution_plan.rs
+/// [memory_pool_tracking.rs]: https://github.com/apache/datafusion/blob/main/datafusion-examples/examples/execution_monitoring/memory_pool_tracking.rs
+/// [memory_pool_execution_plan.rs]: https://github.com/apache/datafusion/blob/main/datafusion-examples/examples/execution_monitoring/memory_pool_execution_plan.rs
 #[derive(Debug)]
 pub struct TrackConsumersPool<I> {
     /// The wrapped memory pool that actually handles reservation logic

datafusion/execution/src/parquet_encryption.rs

@@ -32,7 +32,7 @@ use std::sync::Arc;
 /// integrate with a user's key management service (KMS).
 /// For example usage, see the [`parquet_encrypted_with_kms` example].
 ///
-/// [`parquet_encrypted_with_kms` example]: https://github.com/apache/datafusion/blob/main/datafusion-examples/examples/parquet_encrypted_with_kms.rs
+/// [`parquet_encrypted_with_kms` example]: https://github.com/apache/datafusion/blob/main/datafusion-examples/examples/data_io/parquet_encrypted_with_kms.rs
 #[async_trait]
 pub trait EncryptionFactory: Send + Sync + std::fmt::Debug + 'static {
     /// Generate file encryption properties to use when writing a Parquet file.

datafusion/expr/src/expr.rs

@@ -479,7 +479,7 @@ impl<'a> TreeNodeContainer<'a, Self> for Expr {
 /// that may be missing in the physical data but present in the logical schema.
 /// See the [default_column_values.rs] example implementation.
 ///
-/// [default_column_values.rs]: https://github.com/apache/datafusion/blob/main/datafusion-examples/examples/default_column_values.rs
+/// [default_column_values.rs]: https://github.com/apache/datafusion/blob/main/datafusion-examples/examples/custom_data_source/default_column_values.rs
 pub type SchemaFieldMetadata = std::collections::HashMap<String, String>;
 
 /// Intersects multiple metadata instances for UNION operations.

datafusion/expr/src/simplify.rs

@@ -48,7 +48,7 @@ pub trait SimplifyInfo {
 /// # Example
 /// See the `simplify_demo` in the [`expr_api` example]
 ///
-/// [`expr_api` example]: https://github.com/apache/datafusion/blob/main/datafusion-examples/examples/expr_api.rs
+/// [`expr_api` example]: https://github.com/apache/datafusion/blob/main/datafusion-examples/examples/query_planning/expr_api.rs
 #[derive(Debug, Clone)]
 pub struct SimplifyContext<'a> {
     schema: Option<DFSchemaRef>,

datafusion/expr/src/udaf.rs

@@ -74,8 +74,8 @@ use crate::{Documentation, Signature};
 /// [aggregate function]: https://en.wikipedia.org/wiki/Aggregate_function
 /// [`Accumulator`]: Accumulator
 /// [`create_udaf`]: crate::expr_fn::create_udaf
-/// [`simple_udaf.rs`]: https://github.com/apache/datafusion/blob/main/datafusion-examples/examples/simple_udaf.rs
-/// [`advanced_udaf.rs`]: https://github.com/apache/datafusion/blob/main/datafusion-examples/examples/advanced_udaf.rs
+/// [`simple_udaf.rs`]: https://github.com/apache/datafusion/blob/main/datafusion-examples/examples/udf/simple_udaf.rs
+/// [`advanced_udaf.rs`]: https://github.com/apache/datafusion/blob/main/datafusion-examples/examples/udf/advanced_udaf.rs
 #[derive(Debug, Clone, PartialOrd)]
 pub struct AggregateUDF {
     inner: Arc<dyn AggregateUDFImpl>,
@@ -360,7 +360,7 @@ where
 /// See [`advanced_udaf.rs`] for a full example with complete implementation and
 /// [`AggregateUDF`] for other available options.
 ///
-/// [`advanced_udaf.rs`]: https://github.com/apache/datafusion/blob/main/datafusion-examples/examples/advanced_udaf.rs
+/// [`advanced_udaf.rs`]: https://github.com/apache/datafusion/blob/main/datafusion-examples/examples/udf/advanced_udaf.rs
 ///
 /// # Basic Example
 /// ```

datafusion/expr/src/udf.rs

@@ -57,8 +57,8 @@ use std::sync::Arc;
 /// compatibility with the older API.
 ///
 /// [`create_udf`]: crate::expr_fn::create_udf
-/// [`simple_udf.rs`]: https://github.com/apache/datafusion/blob/main/datafusion-examples/examples/simple_udf.rs
-/// [`advanced_udf.rs`]: https://github.com/apache/datafusion/blob/main/datafusion-examples/examples/advanced_udf.rs
+/// [`simple_udf.rs`]: https://github.com/apache/datafusion/blob/main/datafusion-examples/examples/udf/simple_udf.rs
+/// [`advanced_udf.rs`]: https://github.com/apache/datafusion/blob/main/datafusion-examples/examples/udf/advanced_udf.rs
 #[derive(Debug, Clone)]
 pub struct ScalarUDF {
     inner: Arc<dyn ScalarUDFImpl>,
@@ -413,7 +413,7 @@ pub struct ReturnFieldArgs<'a> {
 /// See [`advanced_udf.rs`] for a full example with complete implementation and
 /// [`ScalarUDF`] for other available options.
 ///
-/// [`advanced_udf.rs`]: https://github.com/apache/datafusion/blob/main/datafusion-examples/examples/advanced_udf.rs
+/// [`advanced_udf.rs`]: https://github.com/apache/datafusion/blob/main/datafusion-examples/examples/udf/advanced_udf.rs
 ///
 /// # Basic Example
 /// ```