Clang: Treat brace initialization as constructor completion

Try to complete constructor after left brace with fallback
to normal completion.

Task-number: QTCREATORBUG-20957
Change-Id: I6c33790a3ee1e623a3d8abe9a44cfd821b6f3106
Reviewed-by: Marco Bubke <marco.bubke@qt.io>

src/plugins/clangcodemodel/clangactivationsequenceprocessor.h

@@ -49,6 +49,7 @@ private:
     void processDot();
     void processComma();
     void processLeftParen();
+    void processLeftBrace();
     void processColonColon();
     void processArrow();
     void processDotStar();