[llvm] [GlobalISel] Add boolean predicated legalization action methods. (PR #111287)

[Thorsten Schütt via llvm-commits]

tschuett wrote:

For the new `legalFor` and `customFor`, I have a slight preference for replacing `For` with `If` . Then it is clear that the first parameter is a predicate and not a type.

https://github.com/llvm/llvm-project/pull/111287