[clang-tidy] Fix crash and handle AttributedType in 'bugprone-easily-swappable-parameters'

@vabridgers identified a way to crash the check by running on code that
involve `AttributedType`s. This patch fixes the check to first and
foremost not crash, but also improves the logic handling qualifiers.

If the types contain any additional (not just CVR) qualifiers that are
not the same, they will not be deemed mixable. The logic for CVR-Mixing
and the `QualifiersMix` check option remain unchanged.

Reviewed By: aaron.ballman, vabridgers

Differential Revision: http://reviews.llvm.org/D106361