boxes: Add API to transform a MetaRectangle

To be used if not a whole region needs to get transformed.
It also has an argument for reverse-transforms.

https://gitlab.gnome.org/GNOME/mutter/merge_requests/366

src/core/boxes-private.h

@@ -24,6 +24,7 @@
 
 #include <glib-object.h>
 
+#include "backends/meta-backend-types.h"
 #include "meta/boxes.h"
 #include "meta/common.h"
 
@@ -245,4 +246,10 @@ meta_rectangle_to_clutter_rect (MetaRectangle *rect)
   };
 }
 
+void meta_rectangle_transform (const MetaRectangle  *rect,
+                               MetaMonitorTransform  transform,
+                               int                   width,
+                               int                   height,
+                               MetaRectangle        *dest);
+
 #endif /* META_BOXES_PRIVATE_H */