This attempts to use the default keymap when the one defined in the
input config fails to compile. The goal is to make it so the keyboard
is always in a usable state, even if it is not the user's requested
settings as usability is more important.
This also removes the calls to `getenv` for the `XKB_DEFAULT_*` family
of environment variables. The reasoning is libxkbcommon will fallback
to using those (and then the system defaults) when any of the rule
names are `NULL` or an empty string anyway so there is no need for
sway to duplicate the efforts.
23c64ab22d