CppTools: Add sourceFilePath to AbstractEditorSupport

Provide the source path to track a generated file source. You can for
example get the modified time stamp for the source file and use it for the
generated file content.

Task-number: QTCREATORBUG-21876
Change-Id: Ia422e128c5cb7a3dce88960f126152c2f65afb41
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@qt.io>

src/plugins/cpptools/abstracteditorsupport.h

@@ -43,6 +43,7 @@ public:
     /// \returns the contents, encoded as UTF-8
     virtual QByteArray contents() const = 0;
     virtual QString fileName() const = 0;
+    virtual QString sourceFileName() const = 0;
 
     void updateDocument();
     void notifyAboutUpdatedContents() const;