wayland/surface: Rename MetaWaylandPendingState to MetaWaylandSurfaceState

The name didn't communicate it was about surface state, and it somewhat
confusingly had the name "pending" in it, which could be confused with
the fact that while it's used to collect pending state, it's also used
to cache previously committed pending state.

https://gitlab.gnome.org/GNOME/mutter/merge_requests/907

src/wayland/meta-wayland-shell-surface.c

@@ -149,7 +149,7 @@ meta_wayland_shell_surface_managed (MetaWaylandShellSurface *shell_surface,
 
 static void
 meta_wayland_shell_surface_surface_commit (MetaWaylandSurfaceRole  *surface_role,
-                                           MetaWaylandPendingState *pending)
+                                           MetaWaylandSurfaceState *pending)
 {
   MetaWaylandActorSurface *actor_surface =
     META_WAYLAND_ACTOR_SURFACE (surface_role);