CppTools: Provide hints about chosen project part for editor document

Parse issues can have multiple reasons (invalid kit, not a project file,
actual parse issue) and we should be able to tell them apart. With this
change, we can distinguish between the fallback project part and a
ambiguous project part.

Follow up changes will use this to display more accurate diagnostics.

Change-Id: Icc8767607cc17dc14d6227b07f34e81ba5525a96
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/cpptools/baseeditordocumentprocessor.cpp

@@ -26,10 +26,10 @@
 #include "baseeditordocumentprocessor.h"
 
 #include "cppcodemodelsettings.h"
-#include "cpplanguage.h"
 #include "cppmodelmanager.h"
 #include "cpptoolsbridge.h"
 #include "cpptoolsreuse.h"
+#include "cpptools_utils.h"
 #include "editordocumenthandle.h"
 
 #include <projectexplorer/session.h>