pointer-constraints: Move min edge distance from backend to Wayland

The min distance to the right/bottom edge depends on Wayland concepts
(wl_fixed_t) and eventually geometry scale. Move the logic the Wayland
side of the pointer constraints machinery to avoid the backend trying to
figure this out without the proper data.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2460>

src/backends/native/meta-backend-native.c

@@ -407,9 +407,14 @@ meta_backend_native_set_pointer_constraint (MetaBackend           *backend,
 
   if (constraint)
     {
+      double min_edge_distance;
+
       region = meta_pointer_constraint_get_region (constraint);
+      min_edge_distance =
+        meta_pointer_constraint_get_min_edge_distance (constraint);
       constraint_impl = meta_pointer_constraint_impl_native_new (constraint,
-                                                                 region);
+                                                                 region,
+                                                                 min_edge_distance);
     }
 
   meta_seat_native_set_pointer_constraint (META_SEAT_NATIVE (seat),