CppTools: Cancel parsing if editor is closed

The m_parserFuture.cancel() in ~BuiltinEditorDocumentProcessor() did not
cancel anything. Thus, closing a document while the parser was running
led to a blocking UI thread.

Now it cancels at the next include directive it encounters.

Change-Id: I092fddbbd747e0bc95265b6e9b4fcc26b3f76cb3
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/plugins/clangcodemodel/clangeditordocumentparser.h

@@ -37,7 +37,8 @@ public:
     ClangEditorDocumentParser(const QString &filePath);
 
 private:
-    void updateHelper(const CppTools::WorkingCopy &) override;
+    void updateHelper(const QFutureInterface<void> &future,
+                      const CppTools::WorkingCopy &) override;
 };
 
 } // namespace ClangCodeModel