This commit moves out non-core wl_surface related code into separate
code units, while renaming types to fit a common scheme. The changes
done are:

 * ClutterActor based surface roles built upon
   MetaWalyandSurfaceRoleActorSurface. This object has been renamed to
   MetaWaylandActorSurface and related functionality has moved into
   meta-wayland-actor-surface.c.

 * The code related to roles backed by a MetaWindow (i.e. built upon
   MetaWaylandShellSurface) was moved into meta-wayland-shell-surface.c

 * The majority of subsurface related code was moved into into
   meta-wayland-subsurface.c and the object was renamed
   MetaWaylandSubsurface.

GNOME/mutter!5
https://bugzilla.gnome.org/show_bug.cgi?id=791938