fix: allow structs in schema provider return types

[agavra]

fixes #5286

Description

This PR allows resolution to a ParamType of StructType for udf methods that have the java return type of Connect's Struct class. The user experience isn't great, as they need to specify the return of the udf using SqlType but the return object as a Connect Struct but that will be follow-up work.

NOTE: The fix is the two lines in UdfUtil, the rest is testing

Testing done

Unit tests

Reviewer checklist

• Ensure docs are updated if necessary. (eg. if a user visible feature is being added or changed).
• Ensure relevant issues are linked (description should include text like "Fixes #")

[vpapavas]

LGTM