feat(core): add Global::create_bind_group_layout_error

[ErichDonGubler]

Description

Some JS runtimes (like Firefox) want to control ID assignment for resources, unconditionally assigning them even when validation rules that has to happen in layers above wgpu-core determine that resources are invalid before even talking to wgpu-core. For these cases, we make wgpu_core::Global::create_*_error APIs, keeping wgpu-core the source of truth for the presence and validity of objects.

The motivation for this PR is that we are missing this for bind group layouts, specifically because of their entries. In WebGPU's WebIDL representation, such entries must have one and only one optional discriminant member specified, indicating which resource type is being used (link). In Rust, we use an enum, and make invalid states unrepresentable. However, for JS, we must (and currently do not) afford wgpu-core users the ability to register invalid bind group layouts for this case, like we do for other APIs (see also the validation listed for GPUDevice.createBindGroupLayout).

Add wgpu_core::Global::create_bind_group_layout_error, which fixes this flaw.

Testing

I don't see other create_*_error APIs tested, and this is consistent with that. This is probably because this sort of API is not something that anything in-tree needs. I've been testing it in Firefox builds, and I believe it works well enough.

Checklist

• If this contains user-facing changes, add a CHANGELOG.md entry.

[ErichDonGubler]

Most of this PR is ready for review, and I don't think review effort would be wasted before I (1) fix up the rustdoc issues firing in CI and (2) update the PR description with spec. link(s).

just don't actually merge it yet plz 🙏🏻