When providing a code-completion suggestion for a hidden name, include

When providing a code-completion suggestion for a hidden name, include
a nested-name-specifier that describes how to refer to that name. For
example, given:

  struct Base { int member; };
  struct Derived : Base { int member; };

the code-completion result for a member access into "Derived" will
provide both "member" to refer to Derived::member (no qualification needed) and
"Base::member" to refer to Base::member (qualification included).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@82476 91177308-0d34-0410-b5e6-96231b3b80d8