WIP: Add the cursor-spy protocol

This protocol spies on cursors. It is required for implementing VNC client side cursor rendering which can significantly improve user experience on high latency connections.

See https://github.com/rfbproto/rfbproto/blob/master/rfbproto.rst#cursor-pseudo-encoding

An implementation in wlroots can be found here: https://github.com/swaywm/wlroots/pull/2329