Add input_nullable for UDAF args StateField and Accumulator

[eejbyfeldt]

Which issue does this PR close?

Part of #8708

Rationale for this change

This is need when we are moving arrag_agg (#11045) to udaf where one of the states nullability will depend on the nullability of the input.

What changes are included in this PR?

This follows how it done for input_type and only provide a single value. But might need to be changed into a Vec in the future.

Are these changes tested?

Existing tests.

Are there any user-facing changes?

New fields in the args struct in UDAF APIs.