Fix binding in generated environment map downsampling pipeline

[ashivaram23]

Objective

When Bevy splits mip generation for environment maps into two passes due to limits, the second pass binds a view to the the original texture when it's supposed to be the 6th mip level of an intermediate one. This causes an error on WebGPU in browsers if that original texture doesn't already have mipmaps.

This affects the atmosphere example on WebGPU, but there are other issues there too so it still won't work after this.

Solution

Create texture view from the texture in the IntermediateTextures component instead of in RenderEnvironmentMap

Testing

Example that doesn't work on WebGPU before this (replace square.png with any power of 2 square image that doesn't store mipmaps)

use bevy::prelude::*;

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_systems(Startup, setup)
        .run();
}

fn setup(
    mut commands: Commands,
    asset_server: Res<AssetServer>,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<StandardMaterial>>,
) {
    commands.spawn((
        Camera3d::default(),
        Transform::from_xyz(0.0, 0.0, 5.0),
        GeneratedEnvironmentMapLight {
            environment_map: asset_server.load("square.png"),
            intensity: 1000.0,
            ..Default::default()
        },
    ));

    commands.spawn((
        Mesh3d(meshes.add(Sphere::new(1.0).mesh().build())),
        MeshMaterial3d(materials.add(StandardMaterial {
            perceptual_roughness: 0.1,
            metallic: 1.0,
            ..Default::default()
        })),
    ));
}

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[mate-h]

Related issue #21700. I can confirm that this fixes the original issue in the browser console for the mip chain, however the example still remains broken due to deferred rendering and SSR.
I tested your branch with the bevy CLI. Leaving these set of commands for other reviewers.

git remote add ashivaram23 https://github.com/ashivaram23/bevy.git
git checkout -b envmap-mip-binding-fix ashivaram23/envmap-mip-binding-fix
bevy run --example atmosphere --features=debug,webgpu web

I noticed that if I disable deferred rendering and SSR the atmosphere example works on web again. So there will need to be another PR for addressing the issue I mentioned. Code change looks good to me!