[CodeComplete] Improve overload handling for C++ qualified and ref-qualified methods.

Summary:
- 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.

Reviewers: ilya-biryukov

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D62582

llvm-svn: 362785