Function validate_texture_copy_range 

pub(crate) fn validate_texture_copy_range<T>(
    texture_copy_view: &TexelCopyTextureInfo<T>,
    desc: &TextureDescriptor<(), Vec<TextureFormat>>,
    texture_side: CopySide,
    copy_size: &Extent3d,
) -> Result<(CopyExtent, u32), TransferError>

WebGPU’s validating texture copy range algorithm.

Copied with minor modifications from WebGPU standard.

Returns the HAL copy extent and the layer count.