Fix specialize_shadows system ordering (#18412)

# Objective
- Fixes #18332

## Solution

- Move specialize_shadows to ManageViews so that it can run after
prepare_lights, so that shadow views exist for specialization.
- Unfortunately this means that specialize_shadows is no longer in
PrepareMeshes like the rest of the specialization systems.

## Testing
- Ran anti_aliasing example, switched between the different AA options,
observed no glitches.

Author: JMS55

crates/bevy_pbr/src/material.rs

@@ -351,9 +351,11 @@ where
                         Render,
                         (
                             check_views_lights_need_specialization.in_set(RenderSet::PrepareAssets),
+                            // specialize_shadows::<M> also needs to run after prepare_assets::<PreparedMaterial<M>>,
+                            // which is fine since ManageViews is after PrepareAssets
                             specialize_shadows::<M>
-                                .in_set(RenderSet::PrepareMeshes)
-                                .after(prepare_assets::<PreparedMaterial<M>>),
+                                .in_set(RenderSet::ManageViews)
+                                .after(prepare_lights),
                             queue_shadows::<M>
                                 .in_set(RenderSet::QueueMeshes)
                                 .after(prepare_assets::<PreparedMaterial<M>>),