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/texteditorconstants.h

@@ -39,6 +39,8 @@ enum TextStyle : quint8 {
     C_SELECTION,
     C_LINE_NUMBER,
     C_SEARCH_RESULT,
+    C_SEARCH_RESULT_ALT1,
+    C_SEARCH_RESULT_ALT2,
     C_SEARCH_SCOPE,
     C_PARENTHESES,
     C_PARENTHESES_MISMATCH,