Clang: Fix highlighting of template function in using declaration

This completes

    commit a3a62e78f7
    Clang: Fix highlighting of function in using declaration

Change-Id: I3c163096374d7a1f45a590bb8ebfe5f5a1f8d417
Reviewed-by: Ivan Donchevskii <ivan.donchevskii@qt.io>
Reviewed-by: Marco Bubke <marco.bubke@qt.io>

tests/unit/unittest/data/highlightingmarks.cpp

@@ -579,3 +579,6 @@ void f32()
 
     NonConstPointerArgument(x.getter());
 }
+
+namespace N { template <typename T> void SizeIs(); }
+using N::SizeIs;