Using region_mapping_id without the desktop portal

If a client connects directly to LIBEI_SOCKET, it cannot map between region_mapping_ids and wayland outputs. For this it would be useful to have a wayland protocol that allows the client to get the mapping id of a wl_output.

Furthermore, such a protocol could allow the compositor to restrict access to LIBEI_SOCKET, instead sending a connected socket via the protocol.

What do you think?