x11/libei: add new port
libei is a library for Emulated Input, primarily aimed at the Wayland
stack. It provides three parts:
- EI (Emulated Input) for the client side (libei)
- EIS (Emulated Input Server) for the server side (libeis)
- oeffis is an optional helper library for DBus communication with the
XDG RemoteDesktop portal (liboeffis)
https://gitlab.freedesktop.org/libinput/libei