Optional xkb config paths should be included

[donfeduardo]

What Happened?

Configuration files in /etc/xkb or ~/.config/xkb are never read. It looks like XkbLayoutHandler.vala reads only a single evdev.xml file (defaulting to the system one in /usr/share/X11/xkb/rules).

Steps to Reproduce

1. Add a new layout or variant in /etc/xkb or ~/.config/xkb. Test it using xkbcli so you know it's valid.
2. Freshly open keyboard settings and try to select the new layout. It won't be there.

Expected Behavior

Keyboard layouts added to one or both of the two other locations searched by libxkbcommon and related tools should be supported.

OS Version

8.x (Circe)

OS Architecture

amd64 (on most hardwares)

Session Type

Secure Session (Wayland, This is the default)

Software Version

Latest release (I have run all updates)

Log Output

Hardware Info

No response

[donfeduardo]

FWIW in my head adding the ability to look at more than just the one evdev.xml also gets you most of the way to improving #169. I'm not sure if it's more sane to slurp up all the various XML files manually and build a tree that way or just to leverage libxkbcommon, but solving this one in the right way reduces #169 to just adding a "show exotic layouts" checkbox to the interface.