C++: Use Token::utf16chars{Begin,End} where appropriate
...especially in CppTools/CppEditor where the offsets are used with a
QString/QTextDocument.
Change-Id: Ic6d18fbc01fb9cc899a9bd2d7424cd2edae487f1
Reviewed-by:
Erik Verbruggen <erik.verbruggen@digia.com>