Core: Allow different highlight colors in search result window

... and make use of that in CppTool's "Find Usages" by assigning
different colors to read and write accesses.

Fixes: QTCREATORBUG-12734
Change-Id: I067db2c8d693bb2c5be44249931ee4f0269f7e52
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>

src/plugins/texteditor/fontsettings.cpp

@@ -151,6 +151,8 @@ static bool isOverlayCategory(TextStyle category)
     return category == C_OCCURRENCES
            || category == C_OCCURRENCES_RENAME
            || category == C_SEARCH_RESULT
+           || category == C_SEARCH_RESULT_ALT1
+           || category == C_SEARCH_RESULT_ALT2
            || category == C_PARENTHESES_MISMATCH;
 }