wayland-server: Expose a getter for global's name

Hi!

I am requesting a getter for a global's name/id as I don't see one already available for the compositors to get this information. Please let me know if there is any good reason not to expose it to compositor (I know that this gets relayed to the wayland client whenever they bind to the global/interface and receive a callback for an event).

In my case, my application is screencast multiple monitors using xdg-desktop-portal APIs. However, when the pipewire streams are started, the only information I get back is the pipewire stream node id and there is no good way to know which pipewire stream node id belongs to which monitor (wayland output). If the compositor could also send back the wayland output's name/id, it can help the application to differentiate between the streams. Towards that end, I was trying to add support to mutter compositor to also return the wayland output id but seems like wayland server doesn't export it right now.

Kindly let me know if exposing the global's name is ok and I can send a small CL for it (which will look pretty similar to the wl_global_get_version getter). Thank you.