This type is intended to replace the scattered functions used to
configure how the Mutter compositor is run. It currently doesn't do
anything, and only has a human readable name, intended to be set to e.g.
"GNOME Shell".
It's an abstract type, and is intended to be used via either a future
`MetaContextMain` for real display server use cases, and a
`MetaContextTest` for test cases.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1861>
