Tweak the code-completion results ranking and formation, so that

Tweak the code-completion results ranking and formation, so that
members found in base classes have the same ranking as members found
in derived classes. However, we will introduce an informative note for
members found in base classes, showing (as a nested-name-specifier)
the qualification to name the base class, to make it clear which
members are from bases.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@82586 91177308-0d34-0410-b5e6-96231b3b80d8