Semantic classification has regressed in master

Method calls, method definitions, property definitions and so on are not correctly highlighted anymore in latest master (compared to 15.7 where the support was restored).

Regression seems to be from this PR: https://github.com/mono/monodevelop/pull/4740

> VS bug [#617341](https://devdiv.visualstudio.com/DevDiv/_workitems/edit/617341)