feat: metadata handling for aggregates and window functions

[timsaucer]

Which issue does this PR close?

• Closes Add metadata support for Aggregate and Window Functions #15902

Rationale for this change

This change is a follow on to #15646. With this change we can now handle metadata for both window and aggregate functions. It enables the use of extension types via this metadata handling.

What changes are included in this PR?

Instead of passing DataType to aggregates and windows we now pass Field in their arguments. return_type has been replaced with return_field so we can get metadata out of these functions as well.

Are these changes tested?

All existing unit tests pass. New unit tests are added.

Are there any user-facing changes?

Yes, the migration guide contains information on the updates that the user will need to make for their user defined functions.

TODO before moving to ready to review

• Add unit test that is a window of an aggregate function
• Verify migration guide covers both aggregate and window functions
• Find remaining places where the function name doesn't match the arguments (ie: fn return_type() that returns a Field)

[timsaucer]

FYI @paleolimbot @crystalxyz since this impacts both of your work

[paleolimbot]

Thank you for this! (Particularly for the heroic updates to all the tests 😬 )

I took a look through and I didn't spot anything out of place (although I'm new to datafusion!).

I'm not sure if the tests are intended to be examples, but it may be worth a slightly more intuitive one (e.g., a sum() that propagates a metadata key unit from the source to the destination).

I also still find it strange to use a Field for these since the name is ignored. Using a dedicated type decoupled from arrow-rs might give you more future flexibility if you need to modify this approach in any way (e.g., to reduce the amount of JSON parsing required when invoking a function on an extension type with parameters). Obviously an optional suggestion!