Since xwayland can only be enabled/disabled at launch, the xwayland
status should be retained on reload. Having `xwayland enabled|disabled`
in the config, should not cause `config->xwayland` to be invalid on
reload. This also returns `CMD_FAILURE` with a message that xwayland
can only be enabled/disabled on launch when trying to set the invalid
status on reload. This allows swaynag to notify the user that the
change will not take effect until sway is restarted.
This commit mostly duplicates the wlr_log functions, although
with a sway_* prefix. (This is very similar to PR #2009.)
However, the logging function no longer needs to be replaceable,
so sway_log_init's second argument is used to set the exit
callback for sway_abort.
wlr_log_init is still invoked in sway/main.c
This commit makes it easier to remove the wlroots dependency for
the helper programs swaymsg, swaybg, swaybar, and swaynag.
Patch tested by compiling with `__attribute__ ((format (printf, 2, 3)))`
applied to `cmd_results_new`.
String usage constants have been converted from pointers to arrays when
encountered. General handler format strings were sometimes modified to
include the old input string, especially for unknown command errors.
