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/symbolscollectorinterface.h

@@ -27,6 +27,7 @@
 
 #include "fileinformation.h"
 #include "symbolentry.h"
+#include "sourcedependency.h"
 #include "sourcelocationentry.h"
 #include "usedmacro.h"
 
@@ -56,6 +57,7 @@ public:
     virtual const FilePathIds &sourceFiles() const = 0;
     virtual const UsedMacros &usedMacros() const = 0;
     virtual const FileInformations &fileInformations() const = 0;
+    virtual const SourceDependencies &sourceDependencies() const = 0;
 };
 
 } // namespace ClangBackEnd