xdg-shell: Add toplevel "bounds" configure event

This aims to communicate the maximum size a surface should be created with, and loosely corresponds to the concept of "work area" in the X11 world.

Closes: #17 (closed)

Signed-off-by: Jonas Ådahl jadahl@gmail.com

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• Reviewer: @emersion
• 3 ACKs:
  • KDE (@zzag)
  • wlroots (@emersion)
  • Mutter/GTK (@jadahl)
• 3 implementations:
  • GTK: https://gitlab.gnome.org/GNOME/gtk/-/merge_requests/4261
  • Mutter: https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2167
  • KWin: https://invent.kde.org/plasma/kwin/-/merge_requests/1808 + https://invent.kde.org/plasma/kwayland-server/-/merge_requests/331