Use SimpleExtensions for Substrait type variations #11544

Describe the bug

Substrait has an extension mechanism for defining things not included in the protobuf format. See https://substrait.io/extensions/#simple-extensions for definition and https://substrait.io/tutorial/sql_to_substrait/#plans for an example (the example only has scalar functions but idea is the same for types and type variations).

DF has been using the extensions for functions, and #11510 adds support for extension types. However DF still uses self-defined consts for type variations (see https://github.com/apache/datafusion/blob/12d82c427d6c37f7884a508707ccd3058a446908/datafusion/substrait/src/variation_const.rs), rather than writing the variations as extensions in the plan. That makes it hard for other producers/consumers to work with DF variations, since they'd need to match the constants, rather than matching by name (+uri).

We should move type variations to also produce simple extensions.

To Reproduce

No response

Expected behavior

No hardcoded references; type variations written as SimpleExtensionDeclarations à la https://github.com/substrait-io/substrait/blob/a68c1ac62f92d703da624cb8ac0cef854dd2b35f/extensions/type_variations.yaml

Additional context

DF also doesn't use the extensionUris mechanism correctly, the field isn't filled and all extensionUriReference are just hardcoded into max u32. That's filed separately as #11545