set uv_transform in pbr_input_from_standard_material (#20783)

Previously, even though the `uv_transform` was being accessed correctly
from the material bindings; that information was not being passed on in
the constructed `pbr_input` from `pbr_input_from_standard_material`.
This led to a situation where the `StandardMaterial` textures would
properly have the `StandardMaterial::uv_transform` applied, but the
`pbr_input.material.uv_transform` value was the default instead of the
material's. In turn this leads to any textures in a material extension
using the wrong uvs, unless the value was accessed from the bindings
directly instead of the pbr_input struct.


## Testing

Given an Affine2 supplied to a StandardMaterial in an extension, such as
this one from the bevy examples

```rust
MeshMaterial3d(materials.add(ExtendedMaterial {
    base: StandardMaterial {
        uv_transform: Affine2::from_scale(
            Vec2::splat(4.),
        ),
        ..Default::default()
    },
    extension: MyExtension::new(1),
})),
```

Previously, accessing the uv_transform from the pbr_input would result
in the default being used, which fills one full cube face.
Accessing from the bindings correctly uses the uv_transform and shows 4
boxes.

```
    // correct
    // let uv = (bevy_pbr::pbr_bindings::material.uv_transform * vec3(in.uv, 1.0)).xy;
    // incorrect
    let uv = (pbr_input.material.uv_transform * vec3(in.uv, 1.0)).xy;

    pbr_input.material.base_color = vec4(uv % 1., 0., 1.);
```

<img width="2560" height="1496" alt="screenshot-2025-08-28-at-06 29
33@2x"
src="https://github.com/user-attachments/assets/e6d843a6-f83b-43a4-aea1-53574f3855a0"
/>

<img width="2560" height="1496" alt="screenshot-2025-08-28-at-06 29
41@2x"
src="https://github.com/user-attachments/assets/e331747c-316a-48ad-be90-e649ca1ca7bf"
/>

Author: ChristopherBiscardi

crates/bevy_pbr/src/render/pbr_fragment.wgsl

@@ -120,6 +120,8 @@ fn pbr_input_from_standard_material(
     let uv_transform = pbr_bindings::material.uv_transform;
 #endif  // BINDLESS
 
+pbr_input.material.uv_transform = uv_transform;
+
 #ifdef VERTEX_UVS_A
     var uv = (uv_transform * vec3(in.uv, 1.0)).xy;
 #endif