Consider changing nullability of UDFs to depend on inputs by default

[Jefffrey]

Is your feature request related to a problem or challenge?

See: #19213 (comment)

Currently nullability is true by default for all UDFs; consider making it depend on input nullabilities (only nullable if inputs are nullable) since that looks to be the more common case. Exception functions would implement it back to true if this behaviour is not desirable.

This is likely to be a notable breaking change so discussion is needed first and the changes would need to be made with care.

Also related:

Describe the solution you'd like

No response

Describe alternatives you've considered

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Additional context

Related:

• Deprecate AggregateUDFImpl::is_nullable in favour of return_field #18882