Clang: Fix recovering on clangbackend crash

The translation unit was updated, but not re-registered.

Handle the editor documents this way:
  1. Reset all ClangEditorDocumentProcessors (this will send an
     unregister message, but that's not problematic).
  2. For the visible editor documents, run their processors so that the
     translation units will be re-registered.
  3. For the invisible editor documents, mark them dirty. Once the user
     makes an invisible document visible again, the processor will run
     and also re-register the translation unit.

Change-Id: I23693ac197bd34a183f3a0020eb5372268636599
Reviewed-by: Marco Bubke <marco.bubke@theqtcompany.com>

src/plugins/cpptools/cppmodelmanager.h

@@ -91,6 +91,7 @@ public:
 
     QFuture<void> updateSourceFiles(const QSet<QString> &sourceFiles,
         ProgressNotificationMode mode = ReservedProgressNotification);
+    void updateCppEditorDocuments() const;
     WorkingCopy workingCopy() const;
     QByteArray codeModelConfiguration() const;
 
@@ -209,7 +210,6 @@ private:
     void initializeModelManagerSupports();
     void delayedGC();
     void recalculateProjectPartMappings();
-    void updateCppEditorDocuments() const;
 
     void replaceSnapshot(const CPlusPlus::Snapshot &newSnapshot);
     void removeFilesFromSnapshot(const QSet<QString> &removedFiles);