shell: add key binding for rotating a surface

Add the key binding Super+Alt+MouseLeftButton to start rotating a
surface by dragging. The rotation is removed, when the drag is near the
rotation origin.

Rotated surface are a stress test for input event coordinate
transformations, damage region tracking, draw transformations, and
window move and resize orientation.

Signed-off-by: Pekka Paalanen <ppaalanen@gmail.com>
diff --git a/src/compositor.h b/src/compositor.h
index 5312665..580800d 100644
--- a/src/compositor.h
+++ b/src/compositor.h
@@ -251,6 +251,9 @@
 };
 
 void
+weston_surface_update_transform(struct weston_surface *surface);
+
+void
 weston_device_repick(struct wl_input_device *device, uint32_t time);
 
 void