DiffEditorPlugin: Add SideBySideDiffOutput

Move generation of SideDiffData into static diffOutput()
method.

Change-Id: Ie38b3e09dd8222e0219fdfb345bc7cf4a39f6e21
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/diffeditor/diffutils.h

@@ -138,6 +138,8 @@ public:
     static QList<FileData> readPatch(const QString &patch,
                                      bool *ok = nullptr,
                                      QFutureInterfaceBase *jobController = nullptr);
+    // For progress reporting
+    static int interpolate(int x, int x1, int x2, int y1, int y2);
 };
 
 } // namespace DiffEditor