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/generatedcodemodelsupport.h

@@ -54,6 +54,7 @@ public:
     /// \returns the contents encoded in UTF-8.
     QByteArray contents() const override;
     QString fileName() const override; // The generated file
+    QString sourceFileName() const override;
 
     static void update(const QList<ProjectExplorer::ExtraCompiler *> &generators);