river: Add experimental map to hide views

mod-Shift-M to switch to an always-unused tag for all connected outputs
to simply hide all application that can currently be seen. Would
probably be more useful with an option to reverse but that probably
requires a more extensive script to implement (perhaps using `lswt`?) so
this will be good enough for now.

I am not even entirely sure how much I will be using it.

wayland/.config/river/init

@@ -115,6 +115,10 @@ riverctl map normal $mod+Control L snap right
 # Mod+F to toggle fullscreen
 riverctl map normal $mod F toggle-fullscreen
 
+# shellcheck disable=SC2016
+# Make all connected outputs show the desktop and no windows at all
+riverctl map normal $mod+Shift M spawn 'for i in $(wlopm | wc -l); do riverctl set-focused-tags $((1 << 10)); riverctl focus-output next; done; riverctl set-focused-tags $((1 << 10)); riverctl focus-output next'
+
 # toggle float
 riverctl map normal $mod+Shift v toggle-float
 # Mod + Left Mouse Button to move views