CppHighlighter: highlight all functions/methods.

- Highlight all function/methods (not just virtual methods).
- Highlight as a function even if number of arguments does not match. In
  that case, add a diagnostic message to indicate there are too many/too
  few arguments.
- Fix highlighting of parameters in function declarations.
  These used to be handled indiferently, and they could be mistaken for
  type or field references.
- Properly highlight template method calls.

Change-Id: I6e61c9ee47763db95c62314f9cc1c4d398df38b3
Reviewed-by: Leandro Melo <leandro.melo@nokia.com>

src/plugins/texteditor/texteditorconstants.h

@@ -60,6 +60,7 @@ enum TextStyle {
     C_FIELD,
     C_STATIC,
     C_VIRTUAL_METHOD,
+    C_FUNCTION,
     C_KEYWORD,
     C_OPERATOR,
     C_PREPROCESSOR,