[libclang] Fix operations (token annotation, getting cursor, etc.) with a file region

inside an objc container that "contains" other file-level declarations.

When getting the array of file-level declarations that overlap with a file region,
we failed to report that the region overlaps with an objc container, if
the container had other file-level declarations declared lexically inside it.

Fix this by marking such declarations as "isTopLevelDeclInObjCContainer" in the AST
and handling them appropriately.

llvm-svn: 145109