testing/font-statusbar: new aport (take two)

This is a replacement for !36830 (closed) with a different approach to the dependency management. (It's also nice to have a fresh start in a new branch given the number of discussions on that one, and the number of times I force-pushed the wrong commits there).

In this incarnation, font-statusbar is... not a package. You can install one of four packages which provide

• a fontconfig that makes "statusbar" point to
  • the patched version of a font with the statusbar ligature icons
  • the donor font (or an equivalent one pulled in by a provider)

(A motivation for this update is that SXMO may be keeping nerd fonts for a while, so we'll want to play nice with this. font-statusbar is (unlike nerdfonts) just a lightweight supplement to a font you probably already have installed, and it's flexible and not too picky).