Session Management Protocol

About

There is a protocol for session management at:

https://gitlab.freedesktop.org/wayland/wayland-protocols/-/merge_requests/18

The overall idea is we have IDs for the session, and for the window. The client flings some IDs to the server, the compositor puts it all together and can then apply a previously saved state by kwin to the window.

We have two IDs, one for the session and one per top-level.

I'll split out some some topics as comments so that we can start some threads.