Dealing with holes in the pipeline layout. #2043

Let's say that for some reason I would like to create a pipeline that only uses bind groups 0 and 2. This could happen for example if I choose BG 1 to be for the fragment data and BG 2 for vertex data, and want to render without an FS. (but many other reasons).

Because GPUPipelineLayoutDescriptor.bindGroupLayout is non-sparse, right now to create the pipeline I need to do the following:

const bgl0 = device.createBindGroupLayout(...);
const bgl2 = device.createBindGroupLayout(...);

const layout = device.createPipelineLayout({
    bindGroupLayouts: [
        bgl0,
        device.createBindGroupLayout({entries: []}), // This is the important part
        bgl2,
    ],
});
const pipeline = ...;

But then to draw with this pipeline I need to set an empty GPUBindGroup at group index 1 to satisfy "validate encoder bindgroups". This is an annoying to just "unset" a bindgroup.

I'd like to suggest that we allow either GPUPipelineLayoutDescriptor.bindGroupLayout to be sparse, or during validation, treat the empty bindgrouplayout the same way as requiring no bind groups.