Allow ignore exclusive for layer shell windows

[Ptitet]

Description

I changed the :exclusive argument for a window from a boolean to an enum to be able to use the "ignore" behavior as described in https://wayland.app/protocols/wlr-layer-shell-unstable-v1#zwlr_layer_surface_v1:request:set_exclusive_zone. This allows the use of Niri's place-within-backdrop layer feature, which only works when the layer exclusive mode is set to -1. This is now possible with the ignore flag.

Usage

(defwindow mywindow
  :monitor 0
  :geometry (geometry
    :x "70px"
    :y "70px"
    :anchor "bottom left"
  )
  :stacking "bg"
  :exclusive "ignore" ; or "exclusive" or "none"
  "hola"
)

Additional Notes

Closes #1415, I have not followed the suggested implementation but I can update accordingly if needed.

Thanks for this amazing tool !
This is one of my first PRs, if I did anything wrong don't hesitate to mention it.

Checklist

Please make sure you can check all the boxes that apply to this PR.

• [N/A] All widgets I've added are correctly documented.
• I added my changes to CHANGELOG.md, if appropriate.
• The documentation in the docs/content/main directory has been adjusted to reflect my changes.
• I used cargo fmt to automatically format all code before committing