Unify ctx_iterator/ctx_begin()/ctx_end() and iterator/begin()/end() so that a...

Unify ctx_iterator/ctx_begin()/ctx_end() and iterator/begin()/end() so that a single iterator type is used for both traversing decls of the same declaration context *and* of the parent declaration contexts, depending on the value of the bool parameter 'LookInParentCtx' that is passed to IdentifierResolver::begin().

llvm-svn: 53724