xserver service: xkbvalidate: Respect `xkb.dir`. Fixes #31138.

Until now, if you set `services.xserver.xkb.dir` to a dir containing
a custom keyboard layout, and making this layout the default via
`services.xserver.xkb.layout`, `xkbvalidate` would complain:

    The value `gb-CapsLockIsHyperL' for keyboard layout is invalid.

    Please check the definition in `services.xserver.xkb.layout'.

    Detailed XKB compiler errors:

        Couldn't find file "symbols/gb-CapsLockIsHyperL" in include paths
        1 include paths searched:
            /nix/store/x1ahkafwzv66s3yxffvrjc0ixkcjiig6-xkeyboard-config-2.31/etc/X11/xkb
        3 include paths could not be added:
            /homeless-shelter/.config/xkb
            /homeless-shelter/.xkb
            /etc/xkb
        Abandoning symbols file "(unnamed)"
        Failed to compile xkb_symbols
        Failed to compile keymap

This is because the `xkb_*()` functions in `xkbvalidate` were not
told to use our `xkbDir`.

This commit fixes it by passing the dir as an environment variable
as described on:

* https://xkbcommon.org/doc/current/group__include-path.html
* https://xkbcommon.org/doc/current/group__context.html

0 files changed, 0 insertions, 0 deletions