Rename the two cursor role types according to the convention used by the
other roles. This means that MetaWaylandSurfaceRoleCursor was renamed to
MetaWaylandCursorSurface, and MetaWaylandSurfaceRoleTabletCursor was
renamed to MetaWaylandTabletCursorSurface. The corresponding filenames
were renamed accordingly too.
https://gitlab.gnome.org/GNOME/mutter/issues/77
This is a simple subclass of MetaWaylandSurfaceRoleCursor, mostly
so we can distinguish by GType, the methods in the parent class
still apply and are useful.