[Variant] Define new shred_variant function (#8366)

# Which issue does this PR close?

- Closes #8361

# Rationale for this change

See ticket.

# What changes are included in this PR?

Define a new `shred_variant` function and implement support for structs
and a subset of primitive types.

# Are these changes tested?

Yes, extensive new unit tests

# Are there any user-facing changes?

The new function is public.

Author: scovich

parquet-variant-compute/Cargo.toml

@@ -34,6 +34,7 @@ rust-version = { workspace = true }
 arrow = { workspace = true }
 arrow-schema = { workspace = true }
 half = { version = "2.1", default-features = false }
+indexmap = "2.10.0"
 parquet-variant = { workspace = true }
 parquet-variant-json = { workspace = true }
 chrono = { workspace = true }

parquet-variant-compute/src/lib.rs

@@ -38,6 +38,7 @@
 mod arrow_to_variant;
 pub mod cast_to_variant;
 mod from_json;
+mod shred_variant;
 mod to_json;
 mod type_conversion;
 mod variant_array;
@@ -50,5 +51,6 @@ pub use variant_array_builder::{VariantArrayBuilder, VariantValueArrayBuilder};
 
 pub use cast_to_variant::{cast_to_variant, cast_to_variant_with_options};
 pub use from_json::json_to_variant;
+pub use shred_variant::shred_variant;
 pub use to_json::variant_to_json;
 pub use type_conversion::CastOptions;