Add xdg-decoration protocol

[HidenoriMatsubayashi]

I don't know that Wayland compositors support xdg-decoration protocol and server-side decoration, but it's better to add xdg-decoration support?

Protocol spec

https://cgit.freedesktop.org/wayland/wayland-protocols/tree/unstable/xdg-decoration/xdg-decoration-unstable-v1.xml

Related information

• GNOME: https://gitlab.gnome.org/GNOME/mutter/-/issues/217
• Wayland-Protocols 1.15 Adds XDG-Decoration Protocol For Server-Side Window Decorations

Note

Wayland-protocol requires version 1.15 or higher.