x11-servers/xlibre-ephyr: New port: Xlibre Xephyr server

Xephyr is a kdrive server that outputs to a window on a pre-existing
'host' X display. Think Xnest but with support for modern extensions
like composite, damage and randr.

Reviewed by: dtxdf acm
Tested by: dtxdf acm
Obtained from: https://github.com/b-aaz/xlibre-ports