Auto merge of rust-lang#13816 - WaffleLapkin:postfix_adjustment_hints, r=Veykril

Postfix adjustment hints

# Basic Description

This PR implements "postfix" adjustment hints:
![2022-12-21_19-27](https://user-images.githubusercontent.com/38225716/208941721-d48d316f-a918-408a-9757-8d4e2b402a66.png)

They are identical to normal adjustment hints, but are rendered _after_ the expression. E.g. `expr.*` instead of `*expr`. ~~This mirrors "postfix deref" feature that I'm planning to eventually propose to the compiler.~~

# Motivation

The advantage of being postfix is that you need to add parentheses less often:

![2022-12-21_19-38](https://user-images.githubusercontent.com/38225716/208944302-16718112-14a4-4438-8aed-797766391c63.png)
![2022-12-21_19-37](https://user-images.githubusercontent.com/38225716/208944281-d9614888-6597-41ee-bf5d-a081d8048f94.png)

This is because a lot of "reborrow" hints are caused by field access or method calls, both of which are postfix and have higher "precedence" than prefix `&` and `*`.

Also IMHO it just looks nicer and it's more clear what is happening (order of operations).

# Modes

However, there are some cases where postfix hints need parentheses but prefix don't (for example `&x` being turned into `(&x).*.*.&` or `&**&x`).

This PR allows users to choose which look they like more. There are 4 options (`rust-analyzer.inlayHints.expressionAdjustmentHints.mode` setting):
- `prefix` — always use prefix hints (default, what was used before that PR)
- `postfix` — always use postfix hints
- `prefer_prefix` — try to minimize number of parentheses, breaking ties in favor of prefix
- `prefer_postfix` — try to minimize number of parentheses, breaking ties in favor of postfix

Comparison of all modes:

![2022-12-21_19-53](https://user-images.githubusercontent.com/38225716/208947482-26357c82-2b42-47d9-acec-835f5f03f6b4.png)
![2022-12-21_19-49](https://user-images.githubusercontent.com/38225716/208946731-fe566d3b-52b2-4846-994d-c2cecc769e0f.png)
![2022-12-21_19-48](https://user-images.githubusercontent.com/38225716/208946742-6e237f44-805e-469a-a3db-03d8f76e1317.png)
![2022-12-21_19-47](https://user-images.githubusercontent.com/38225716/208946747-79f25fae-e3ea-47d2-8d27-cb4eeac034fe.png)

# Edge cases

Where are some rare cases where chain hints weirdly interact with adjustment hints, for example (note `SourceAnalyzer.&`):

![image](https://user-images.githubusercontent.com/38225716/208947958-41c12971-f1f0-4a41-a930-47939cce9f58.png)

This is pre-existing, you can get the same effect with prefix hints (`SourceAnalyzer)`).

----

Another weird thing is this:

![2022-12-21_20-00](https://user-images.githubusercontent.com/38225716/208948590-ea26d325-2108-4b35-abaa-716a65a1ae99.png)

Here `.&` is a hint and `?` is written in the source code. It looks like `?` is part of the hint because `?.` is ligature in my font. IMO this is a bug in vscode, but still worth mentioning (I'm also too lazy to report it there...).

# Fixed bugs

I've used the "needs parens" API and this accidentally fixed a bug with parens around `as`, see the test diff:
```diff,rust
     let _: *const u32  = &mut 0u32 as *mut u32;
                        //^^^^^^^^^^^^^^^^^^^^^<mut-ptr-to-const-ptr>
+                       //^^^^^^^^^^^^^^^^^^^^^(
+                       //^^^^^^^^^^^^^^^^^^^^^)
...
     let _: *const u32  = &mut 0u32 as *mut u32;
                        //^^^^^^^^^^^^^^^^^^^^^<mut-ptr-to-const-ptr>
+                       //^^^^^^^^^^^^^^^^^^^^^(
+                       //^^^^^^^^^^^^^^^^^^^^^)
```

# Changelog

changelog feature Add an option to make adjustment hints (aka reborrow hints) postfix
changelog fix Fix placement of parentheses around `as` casts for adjustment hints

Author: bors

crates/ide/src/inlay_hints.rs

@@ -35,6 +35,7 @@ pub struct InlayHintsConfig {
     pub parameter_hints: bool,
     pub chaining_hints: bool,
     pub adjustment_hints: AdjustmentHints,
+    pub adjustment_hints_mode: AdjustmentHintsMode,
     pub adjustment_hints_hide_outside_unsafe: bool,
     pub closure_return_type_hints: ClosureReturnTypeHints,
     pub binding_mode_hints: bool,
@@ -74,6 +75,14 @@ pub enum AdjustmentHints {
     Never,
 }
 
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum AdjustmentHintsMode {
+    Prefix,
+    Postfix,
+    PreferPrefix,
+    PreferPostfix,
+}
+
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub enum InlayKind {
     BindingModeHint,
@@ -82,6 +91,7 @@ pub enum InlayKind {
     ClosureReturnTypeHint,
     GenericParamListHint,
     AdjustmentHint,
+    AdjustmentHintPostfix,
     LifetimeHint,
     ParameterHint,
     TypeHint,
@@ -430,7 +440,7 @@ mod tests {
     use itertools::Itertools;
     use test_utils::extract_annotations;
 
-    use crate::inlay_hints::AdjustmentHints;
+    use crate::inlay_hints::{AdjustmentHints, AdjustmentHintsMode};
     use crate::DiscriminantHints;
     use crate::{fixture, inlay_hints::InlayHintsConfig, LifetimeElisionHints};
 
@@ -446,6 +456,7 @@ mod tests {
         lifetime_elision_hints: LifetimeElisionHints::Never,
         closure_return_type_hints: ClosureReturnTypeHints::Never,
         adjustment_hints: AdjustmentHints::Never,
+        adjustment_hints_mode: AdjustmentHintsMode::Prefix,
         adjustment_hints_hide_outside_unsafe: false,
         binding_mode_hints: false,
         hide_named_constructor_hints: false,