[Variant] Preserve UUID extension type metadata for Parquet writer

[sdf-jkl]

Which issue does this PR close?

• Closes #NNN.

Rationale for this change

Shredding into FixedSizeBinary(16) means we're shredding into UUID Parquet logical type. shred_variant currently doesn't preserve extension type metadata for the typed value field.

UUID is the only valid Variant shredding type that requires an arrow extension type. https://github.com/apache/parquet-format/blob/master/VariantShredding.md

Earlier in # @scovich mentioned:

Yeah, as long as shred_variant only takes a DataType instead of a Field, we are forced to assume 16-byte fixed binary is UUID. If it accepted a Field, we should additionally require the UUID extension type. Otherwise, we potentially run into problems because Decimal128 can also use 16-byte fixed binary!

This is an argument proposing to use Field instead of DataType for as_type parameter in shred_variant. This should not be an issue because arrow has a Decimal128Type to represent Decimal128 logical Parquet type. This way there's no ambiguity in using FixedSizeBinary(16) arrow type to represent UUID. Switching as_type to Field is unnecessary.

What changes are included in this PR?

• VariantArray::from_parts/ShreddedVariantFieldArray::from_parts now add UUID extension type metadata to the typed_value Field if DataType is FixedSizeBinary(16)
• Uncommented UUID extension part metadata validation in a unit test.

Are these changes tested?

• Yes, unit test.

Are there any user-facing changes?

• Shredded UUID typed value fields now preserve UUID extension type metadata.