Avoid use of Signature::user_defined for normal functions

[findepi]

Originally posted by @alamb in #12698 (comment)

Can we make it a goal that not to require Signature::user_defined to implement useful things?

Yes, I think this should be the goal

The usecase for Signature::user_defined that I recall was to implement coercion rules for very specific functions (like coalesce)

Extend signatures and function resolution so that Signature::user_defined is not needed.

[jayzhan211]

Before #12622 is completed, we can introduce signature like Numeric / String / Float / Integer and so on that is used in places more than 1, others use Signature::user_defined by default