CppEditor: Fix go to definition of macros.

- Go to macro definition only on macro name (ie not in parameters).
- Prefer macro definition over expanded code definition, as the
  preprocessor is executed first: when trying to go to definition, the
  user sees the macro, not the expanded code.

Task-number: QTCREATORBUG-2240
Task-number: QTCREATORBUG-6175
Task-number: QTCREATORBUG-6848
Task-number: QTCREATORBUG-7008
Task-number: QTCREATORBUG-7009

Change-Id: I819c763524e79b20518c26a46a99a3a3b0a131bd
Reviewed-by: Andre Hartmann <aha_1980@gmx.de>
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: Erik Verbruggen <erik.verbruggen@nokia.com>