irradiance: use textureSampleLevel for WebGPU support (#11893)

# Objective

- Fixes #11879 

## Solution

- Use `textureSampleLevel` instead of `textureSample`

Co-authored-by: Griffin <33357138+DGriffin91@users.noreply.github.com>

Author: mockersf

crates/bevy_pbr/src/light_probe/irradiance_volume.wgsl

@@ -42,9 +42,9 @@ fn irradiance_volume_light(world_position: vec3<f32>, N: vec3<f32>) -> vec3<f32>
     let uvw_y = uvw + vec3(0.0f, neg_offset.y, 1.0f / 3.0f);
     let uvw_z = uvw + vec3(0.0f, neg_offset.z, 2.0f / 3.0f);
 
-    let rgb_x = textureSample(irradiance_volume_texture, irradiance_volume_sampler, uvw_x).rgb;
-    let rgb_y = textureSample(irradiance_volume_texture, irradiance_volume_sampler, uvw_y).rgb;
-    let rgb_z = textureSample(irradiance_volume_texture, irradiance_volume_sampler, uvw_z).rgb;
+    let rgb_x = textureSampleLevel(irradiance_volume_texture, irradiance_volume_sampler, uvw_x, 0.0).rgb;
+    let rgb_y = textureSampleLevel(irradiance_volume_texture, irradiance_volume_sampler, uvw_y, 0.0).rgb;
+    let rgb_z = textureSampleLevel(irradiance_volume_texture, irradiance_volume_sampler, uvw_z, 0.0).rgb;
 
     // Use Valve's formula to sample.
     let NN = N * N;