[libclang] indexing: handle 'TopLevelDeclInObjCContainers' at the point where they are reported.

It isn't much benefit and doesn't worth the complexity to try to handle them after the container is encountered.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@260254 91177308-0d34-0410-b5e6-96231b3b80d8