More panel options

[robin-carlier]

I finally found some time to implement what we discussed (and a bit more) in #8007

The main additions/modifications are

• A new --layer option for the kitten panel to specify on which layer the panel should be drawn.
• A new --edge=none option for the kitten, when set, the width, height and margins of the kitten can be freely set to get some flexibility in the geometry. When set, the panel leaves its exclusive_zone to -1, so it might get drawn on top of other things. Maybe we could also add a flag to conthol this as well?
• --lines and --colums are now split as two distinct parameters to control the size (in cells) when using --edge=none.
• New --margin-... options to set some margin if desired.
• New focus-policy flag.

With this, I think the kitten should be reasonably flexible to be used in fun ways.

I could test that the options behave as expected using Hyprland, but I don’t know if they do for other compositors.

[kovidgoyal]

I am fine with adding a flag to control exclusive_zone.

[robin-carlier]

I am fine with adding a flag to control exclusive_zone.

I split it into two flags: override-exclusive-zone to allow override for panels anchored through e.g, edge=top, and a exclusive-zone flag to actually pass the value in case it is overriden.

[kovidgoyal]

Merged. It might be good to add some "recipes" or cookbook style
examples for doing common things to the docs for the panel kitten in
docs/kittens/panel.rst