x11/wmenu: New port

wmenu is an efficient dynamic menu for Sway and wlroots based Wayland
compositors. It provides a Wayland-native dmenu replacement which
maintains the look and feel of dmenu.

https://sr.ht/~adnano/wmenu

PR:		269693
Reviewed by:	diizzy, jbeich
Differential Revision:	https://reviews.freebsd.org/D39230