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/libs/3rdparty/cplusplus/Lexer.cpp

@@ -36,6 +36,21 @@ using namespace CPlusPlus;
     \sa Token
 */
 
+/*!
+    \fn static void Lexer::yyinp_utf8(const char *&currentSourceChar, unsigned char &yychar, unsigned &utf16charCounter)
+
+    Process a single unicode code point in an UTF-8 encoded source.
+
+    \a currentSourceChar points to the UTF-8 encoded source.
+    \a yychar must be the byte pointed to by \a currentSourceChar.
+
+    Points \a currentSourceChar to the byte of the next code point
+    and modifies \a yychar to the value pointed by the updated
+    \a currentSourceChar. \a utf16charCounter will be incremented by
+    the number of UTF-16 code units that were needed for that code
+    point.
+*/
+
 Lexer::Lexer(TranslationUnit *unit)
     : _translationUnit(unit),
       _control(unit->control()),