Add concrete types to the `image` and `mipmaps` properties of Texture

[mewore]

Describe the feature you'd like:

https://github.com/three-types/three-ts-types/blob/6a5f78138c10ca144f15f4e3ea3b989c60f307d1/types/three/src/textures/Texture.d.ts#L52 https://github.com/three-types/three-ts-types/blob/6a5f78138c10ca144f15f4e3ea3b989c60f307d1/types/three/src/textures/Texture.d.ts#L57 If it's certain that these are the only types they can have, then they can be added to the type declaration itself.

However, note that this is a breaking change for the transpilation of TS code which directly uses any sub-properties of these properties (except .image.width and .image.height, which are always present) or casts one of them to an unrelated type.

Suggested implementation:

    /**
     * @default THREE.Texture.DEFAULT_IMAGE
     */
    image: HTMLImageElement | ImageData | {width: number, height: number};

    /**
     * The array of the texture mipmaps ({@link ImageData} for 2D textures and {@link CubeTexture} for cube textures).
     * 
     * @default []
     */
    mipmaps: ImageData[] | CubeTexture[];

This is based on my understanding that if it's a 2D texture, then all of its mipmaps are of type ImageData, and if it's a cube texture, then all of its mipmaps are of type CubeTexture. If I'm wrong, then it should be mipmaps: (ImageData | CubeTexture)[] instead.

[capnmidnight]

The image field for a Texture can actually be a lot of different things. Just the raw types that WebGL can accept as a texture source alone are:

• HTMImageElement
• HTMLVideoElement
• HTMLCanvasElement
• OffscreenCanvas
• ImageData
• ImageBitmap

There is a type in lib.d.ts called TexImageSource that unions all of these types together.

But Three.js also has a few hacks in place where they use the image field to track the dimensions of the texture without actually storing a TexImageSource. As you've noted in your suggestion, a width/height object is one case (CompressedTexture, DepthTexture, and FramebufferTexture). But also, CubeTexture allows for an array of images, DataTexture is similar to CompressedTexture with an additional data field, Data3DTexture and DataArrayTexture are similar to DataTexture with an additional depth field,

It seems, in all cases except CubeTexture, the images field will always have at least { width: number; height: number; }. But that on its own wouldn't be too helpful and it's not clear what the most accurate way to type all of this would be.

Perhaps it is necessary to break from trying to 1-to-1 mirror the exported Texture types of Three.js and introduce a new interface, some kind of BaseTexture, that has the maximal union of all types that image can take, and then change the concrete class definitions to extend BaseTexture with more restrained types for their respective parameters.

[capnmidnight]

IDK, maybe something like this? I added some generic type parameters to Texture, that should be able to accept any of those hack cases, plus with a default setting of TexImageSource. The other subclasses of Texture then define a more meaningful value for their case.

https://github.com/capnmidnight/three-ts-types/commit/799005085b7b3ad303d579b7b6f17fc22bcf43c8

I'm not too sure about the mipmaps field, so I haven't submitted this as a PR. Maybe someone else has some insight here?