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/cpptools.pro

@@ -34,7 +34,6 @@ HEADERS += \
     cppfunctionsfilter.h \
     cppincludesfilter.h \
     cppindexingsupport.h \
-    cpplanguage.h \
     cpplocalsymbols.h \
     cpplocatordata.h \
     cpplocatorfilter.h \
@@ -50,6 +49,7 @@ HEADERS += \
     cppsemanticinfoupdater.h \
     cppsourceprocessor.h \
     cpptools_global.h \
+    cpptools_utils.h \
     cpptoolsconstants.h \
     cpptoolsjsextension.h \
     cpptoolsplugin.h \