deno: Fix error reporting for async pipeline creation

[andyleiserson]

Of createRenderPipelineAsync, the spec says:

If pipeline creation fails, the returned Promise rejects with an GPUPipelineError. (A GPUError is not dispatched to the device.)

This changes the deno bindings to do as it says.

Ancillary note: Since pipeline creation is not actually async, the only reason to use these functions would be to follow the spec's recommendation that they are preferred, possibly in hopes of a future performance improvement.

To simplify the pipeline creation functions, this change also adds some WebIDL converters, which eliminates an explicit error return from new_render_pipeline. These changes are in separate commits.

Testing
By the CTS.

Squash or Rebase? Rebase (after squashing any fixups)

Checklist

• Run cargo fmt.
• Run taplo format.
• Run cargo clippy --tests. If applicable, add:
  • --target wasm32-unknown-unknown
• Run cargo xtask test to run tests.
• This might be salient for a Deno changelog, but doesn't seem important to note in the wgpu changelog.