COSMIC DE: Tiling redesign and libcosmic rebasing

It's been interesting watching System76 work on this. Can't say I love their aesthetics but the concepts look sound.

I don't use tiling, but always good to see COSMIC coming along nicely with these updates.

I never got comfortable with tiling extensions on Gnome since they always had annoying bugs (crashes, floating windows hiding behind tiled windows, not resising correctly). Sway or Hyprland work flawlessly, with tiling directly built in the compositor. Hopefully Cosmic DE's compositor will manage to tile like sway, because then I'll seriously consider switching.

Tiling isn't a feature that I use to any degree. However, I'm really excited to see the progress you've made on the DE. I'll definitely give it a spin when it's released.