Use return_field_from_args in information schema and date_trunc

[AndreaBozzo]

Which issue does this PR close?

• Closes Information schema should use return_field_from_args #19870.

Rationale for this change

Some UDFs/UDAFs implement return_field_from_args / return_field instead of return_type. The information schema was calling return_type directly, which fails for those functions. The default implementation of return_field_from_args already delegates to return_type, so switching to the newer API works for all functions.

What changes are included in this PR?

• information_schema.rs: get_udf_args_and_return_types now calls return_field_from_args instead of return_type; get_udaf_args_and_return_types now calls return_field instead of return_type. Removed stale comments referencing the old API.
• date_trunc.rs: return_type now returns internal_err, and return_field_from_args is self-contained (no longer delegates to return_type), following the same pattern as other UDFs like named_struct and map_from_arrays (ref: fix: derive custom nullability for spark map_from_arrays #19275).

Are these changes tested?

Covered by existing information_schema sqllogictests and datafusion-functions unit tests.

Are there any user-facing changes?

No.