C++: Add utf16 indices to Macro and Document::MacroUse

In most cases we need to work with the utf16 indices. Only in
cppfindreferences the byte interface is still needed since there we read
in files and work on a QByteArray to save memory.

Change-Id: I6ef6a93fc1875a8c9a305c075d51a9ca034c41bb
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>

src/plugins/cpptools/cppcompletionassist.cpp

@@ -1751,7 +1751,7 @@ void CppCompletionAssistProcessor::addMacros_helper(const CPlusPlus::Snapshot &s
         addMacros_helper(snapshot, i.resolvedFileName(), processed, definedMacros);
 
     foreach (const Macro &macro, doc->definedMacros()) {
-        const QString macroName = QString::fromUtf8(macro.name().constData(), macro.name().length());
+        const QString macroName = macro.nameToQString();
         if (!macro.isHidden())
             definedMacros->insert(macroName);
         else