When we're predicting state, i.e. when having posted an update while
avoiding reading KMS state, copy the predicted state, update the actual
state, and check that the predicted state matches the newly updated one.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2159>
As other KMS tests, depends on being DRM master and vkms being loaded.
Currently consists of a sanity check that checks for the expected set of
connectors, CRTCs, planes, etc.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2159>