wayland: add support for the xdg toplevel tag protocol

It allows applications to tag their windows with a name, like "main window", "email composer", "pip video" or similar, which the compositor can use for window rules or restoring state of application windows without xdg session management support.

We also (optionally) get a translated window description, which we could use for accessibility purposes later on.

Wayland-protocols MR: https://gitlab.freedesktop.org/wayland/wayland-protocols/-/merge_requests/238