Clang: Collect source dependencies

It is quite easy because we track the include directives in the
preprocessor callbacks.

Change-Id: I2d7bd67b31f50c0d8d4a46c57e83dffa0c558dc7
Reviewed-by: Ivan Donchevskii <ivan.donchevskii@qt.io>

src/tools/clangrefactoringbackend/source/symbolscollector.h

@@ -53,6 +53,7 @@ public:
     const FilePathIds &sourceFiles() const override;
     const UsedMacros &usedMacros() const override;
     const FileInformations &fileInformations() const override;
+    const SourceDependencies &sourceDependencies() const override;
 
 private:
     ClangTool m_clangTool;