Mk/Uses/xorg-cat.mk: Resurrect CATEGORIES=proto and switch EXTRACT_SUFX to xz
Resurrect CATEGORIES=proto to simplify the port's Makefile.
Remove experimental from the meson's comment, as some ports have fully
transitioned to building with Meson.
Upstream has switched from bz2 to xz, so update EXTRACT_SUFX.
PR: 298092
Approved by: x11 (arrowd)
Approved by: fluffy (mentor)