Fix solari GI shadow regression (#21919)

In #21649, I switched where
visibility rays get traced, and while it improved DI, it regressed GI.
I'm reverting the GI change to fix.

Before:
<img width="3206" height="1875" alt="image"
src="https://github.com/user-attachments/assets/379c613a-2a36-4fe0-81f1-9e278b28ca37"
/>

After:
<img width="3206" height="1875" alt="image"
src="https://github.com/user-attachments/assets/56f5c457-6639-4b48-9472-8cd2ad4936d8"
/>

Author: JMS55

crates/bevy_solari/src/realtime/restir_gi.wgsl

@@ -67,9 +67,7 @@ fn spatial_and_shade(@builtin(global_invocation_id) global_id: vec3<u32>) {
     let spatial = load_spatial_reservoir(global_id.xy, depth, surface.world_position, surface.world_normal, &rng);
     let merge_result = merge_reservoirs(input_reservoir, surface.world_position, surface.world_normal, surface.material.base_color / PI,
         spatial.reservoir, spatial.world_position, spatial.world_normal, spatial.diffuse_brdf, &rng);
-    var combined_reservoir = merge_result.merged_reservoir;
-
-    combined_reservoir.radiance *= trace_point_visibility(surface.world_position, combined_reservoir.sample_point_world_position);
+    let combined_reservoir = merge_result.merged_reservoir;
 
     gi_reservoirs_a[pixel_index] = combined_reservoir;
 
@@ -164,7 +162,9 @@ fn load_spatial_reservoir(pixel_id: vec2<u32>, depth: f32, world_position: vec3<
     }
 
     let spatial_pixel_index = spatial_pixel_id.x + spatial_pixel_id.y * u32(view.main_pass_viewport.z);
-    let spatial_reservoir = gi_reservoirs_b[spatial_pixel_index];
+    var spatial_reservoir = gi_reservoirs_b[spatial_pixel_index];
+
+    spatial_reservoir.radiance *= trace_point_visibility(world_position, spatial_reservoir.sample_point_world_position);
 
     return NeighborInfo(spatial_reservoir, spatial_surface.world_position, spatial_surface.world_normal, spatial_diffuse_brdf);
 }