[Clang] Fix member lookup so that we don't ignore ambiguous lookups in some cases

There are some cases during member lookup we are aggressively suppressing
diagnostics when we should just be suppressing access control diagnostic.

In this PR I add the ability to simply suppress access diagnostics while not
suppressing ambiguous lookup diagnostics.

Fixes: https://github.com/llvm/llvm-project/issues/22413
https://github.com/llvm/llvm-project/issues/29942
https://github.com/llvm/llvm-project/issues/35574
https://github.com/llvm/llvm-project/issues/27224

Differential Revision: https://reviews.llvm.org/D155387