Investigate adding a gdk-raw-window-handle crate

[bilelmoussaoui]

A crate that would implement the traits provided by raw-window-handle for the various gdk backends (wayland/x11/macos/win32)

[bilelmoussaoui]

Ideally we would want to have gdk4-macos around first

[bilelmoussaoui]

wayland/x11 part is already handled in https://github.com/bilelmoussaoui/ashpd/blob/master/src/window_identifier/gtk4.rs#L86-L113 btw