Add toggle logic inside DPMS handler

[ivanfed0t0v]

Logic that obtains current DPMS state is put inside the handler.

sway_output from which the current DPMS state will be obtained is selected by the following logic:

• For - and -- the focused output is used;
• For * error "Cannot apply toggle to all outputs" is reported;
• For everything else all_output_by_name_or_id() is used.

Fixes #5929.

[ivanfed0t0v]

Test cases:

• $ swaymsg output <output> dpms toggle - should successfully toggle specified output.

On multi monitor setup:

• $ swaymsg output - dpms toggle - should toggle just focused output.
• $ swaymsg output * dpms toggle - should print "Cannot apply toggle to all outputs." and exit.
• $ swaymsg output * dpms on - should work and not print any errors.
• $ swaymsg output <unknown-output> dpms toggle - should print "Cannot apply toggle to unknown output".

[rpigott]

Hi, thanks for the PR.

The new intended behavior makes sense to me, at least. I doubt it would make much sense to toggle each output state individually.

[ivanfed0t0v]

I doubt it would make much sense to toggle each output state individually.

I agree and I don't think it's currently possible to toggle DPMS on each output individually from inside the handler anyway.

Actually, handler at output/toggle.c simply reports an error when called on wildcard. I think I should do the same with DPMS for consistency.

[rpigott]

Just one small thing – now that dpms has a "toggle" argument could you please add it to the sway-output man page? I think the meaning is clear, so just listing on|off|toggle for the argument of dpms is probably fine.

Other than that, this LGTM. Should probably be squashed for merging.

[emersion]

Looks good to me, and it seems like @rpigott is fine with this version too.

Thanks!