[CodeComplete] Improve overload handling for C++ qualified and ref-qualified methods.
- when a method is not available because of the target value kind (e.g. an && method on a Foo& variable), then don't offer it.
- when a method is effectively shadowed by another method from the same class with a) an identical argument list and b) superior qualifiers, then don't offer it.
Differential Revision: https://reviews.llvm.org/D62582