Add a setting to ImageLoader that calls Image::reinterpret_stacked_2d_as_array

[grind086]

Objective

If you want to use a TilemapChunk (or more generally use a texture2DArray in a shader), you have to implement a mechanism that waits for your texture to load, then calls Image::reinterpret_stacked_2d_as_array.

Solution

Have the loader do it instead.

Closes #20799, which does very similar things and should be remade if more functionality is needed.

Testing

• Ran the updated examples

---

Showcase

let array_texture = asset_server.load_with_settings(
    "textures/array_texture.png",
    |settings: &mut ImageLoaderSettings| {
        settings.array_layout = Some(ImageArrayLayout::RowCount(4));
    },
);

[alice-i-cecile]

I like this change! A few things:

• I think we can make the enum clearer
• this is a neat change, but not splashy enough for a release note
• this needs a short migration guide for the new field on ImageLoaderSettings

[github-actions]

It looks like your PR is a breaking change, but you didn't provide a migration guide.

Please review the instructions for writing migration guides, then expand or revise the content in the migration guides directory to reflect your changes.

[KirmesBude]

This tries to do something similar. At least the motivation is the same #20799

[grind086]

I went ahead and applied the suggested changes, but I would be fine closing in favor of #20799 if you'd prefer that one.

[alice-i-cecile]

I'm happy with this now, but I'll defer to you and @KirmesBude on which solution you prefer.

[KirmesBude]

@alice-i-cecile @grind086 My PR does more (cubemap), but that does not mean it does it better. I only really care about 2darray anyways and this PR does exactly that, so we can go ahead with this one. Thanks for creating the PR :).