Factor out surface rotation into protocol?

In 460099f1 (2012) @pq added the uber cool feature to rotate surfaces with Super+MouseLeftButton, presumably as a "stress test for input event coordinate transformations, damage region tracking, draw transformations, and window move and resize orientation". Beyond that, it is a generally cool feature that can be useful at times, and it would be nice if it could find its way to the general wayland ecosystems by means of a proper protocol. The only other compositor that seems to provide something like this up to now is wayfire with its wrot plugin https://github.com/WayfireWM/wayfire/wiki/Configuration#window-rotate, that however is supposedly also capable of 3D transformations.