Changes

[clang][cli] Add flexible TableGen multiclass for boolean options

This introduces more flexible multiclass for declaring two flags controlling the same boolean keypath.

Compared to existing Opt{In,Out}FFlag multiclasses, the new syntax makes it easier to read option declarations and reason about the keypath.

This also makes specifying common properties of both flags possible.

I'm open to suggestions on the class names. Not 100% sure the benefits are worth the added complexity.

Depends on D92774.

Reviewed By: dexonsmith

Differential Revision: https://reviews.llvm.org/D92775