Add TilemapChunk rendering

[ConnerPetzold]

Objective

An attempt to start building a base for first-party tilemaps (#13782).

The objective is to create a very simple tilemap chunk rendering plugin that can be used as a building block for 3rd-party tilemap crates, and eventually a first-party tilemap implementation.

Solution

• Introduces two user-facing components, TilemapChunk and TilemapChunkIndices, and a new material TilemapChunkMaterial.
• TilemapChunk holds the chunk and tile sizes, and the tileset image
  • The tileset image is expected to be a layered image for use with texture_2d_array, with the assumption that atlases or multiple images would go through an asset loader/processor. Not sure if that should be part of this PR or not..
• TilemapChunkIndices holds a 1d representation of all of the tile's Option index into the tileset image.
  • Indices are fixed to the size of tiles in a chunk (though maybe this should just be an assertion instead?)
  • Indices are cloned and sent to the shader through a u32 texture.

Testing

• Initial testing done with the tilemap_chunk example, though I need to include some way to update indices as part of it.
• Tested wasm with webgl2 and webgpu
• I'm thinking it would probably be good to do some basic perf testing.

---

Showcase

let chunk_size = UVec2::splat(64);
let tile_size = UVec2::splat(16);
let indices: Vec<Option<u32>> = (0..chunk_size.x * chunk_size.y)
    .map(|_| rng.gen_range(0..5))
    .map(|i| if i == 0 { None } else { Some(i - 1) })
    .collect();

commands.spawn((
    TilemapChunk {
        chunk_size,
        tile_size,
        tileset,
    },
    TilemapChunkIndices(indices),
));

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[StarArawn]

Correct me if I'm wrong but I don't think ShaderStorageBuffer's work on webGL.

[ConnerPetzold]

@StarArawn good call -- updated to use a u32 texture instead. I think it may be better to use vertex attributes like you do with ecs_tilemap, but I'm not sure of the tradeoffs. I suspect using the vertex attributes and shader are necessary for making non-square tiles work?

[ConnerPetzold]

Here's a prototype 3rd-party crate that utilizes the changes here: https://github.com/ConnerPetzold/bevy_tilemap/tree/main/src

[IceSentry]

I added a few comments, once those are fixed I think it will be good to merge.

Thank you for working on this!

[ConnerPetzold]

Should this be TilemapChunkMeshCache to align better with other names in Bevy?