* Use () instead of PhantomData as IdentityManager's Input type.
PhantomData suggests that there's some sort of persuasion required
for lifetime variance inference or other sorts of arcana, but it
doesn't seem to be necessary at all. `()` works just fine.
* Make the color attachments `Option`-al in render pipelines, render passes, and render bundles
* vk: `Option`-al color attachments support
* dx12: sparse color_attachments support
* Only non-hole attachments is supported on wasm target and gl backend
* deno_webgpu: `Option`-al color attachments support
* Follow all suggestions
