WIP workspace v2, based on ext-workspace

[ids1024]

Needs cctk changes, and cosmic-comp support.

Updating the cctk abstraction handle both protocols may be a bit awkward. Perhaps like #46, it needs an enum wrapper over handles. Workspace.state could be changed to the ext type. While capabilities needs to be wrapped/split in some way.

This requires changes to the toplevel_info/toplevel_management protocols to use ext handles.

[Drakulix]

Since all our clients use cctk I think the way to proceed here is to change cosmic-comp to support both v1 and v2 as well as ext-workspace and then just transition clients over from v1 to v2 (making sure the cctk implementation works as well as it can, if only ext-workspace is available).

I don't think the clients need to handle the old version anymore, once we released cosmic-comp with v2 support.

[ids1024]

Yeah, that may be best here. Then it can just be updated similarly to #49 to require ext-workspace, and optionally the cosmic extension.