Make Tests that check limits skip optional limits

[greggman]

Currently, src/webgpu/capability_info.ts has a list of limits and src/webgpu/api/operation/adapter/requestDevice.spec.ts and src/webgpu/idl/javascript.spec.ts requires those limits to exist AND no others.

Decide how deal with this.

IMO The CTS should test the spec. An implementation that is exposing things that are not yet part of the spec is a non-conforming implementation and should fail conformance.

At the same time, it would be nice of some tests didn't fail when new limits are experimented with.

decide what to do

[kainino0x]

Personally I think we should test it. A failing test lets the browsers decide how they want to handle it.

For example in Chromium we run CTS with --enable-unsafe-webgpu which exposes extra stuff. We'll just suppress the tests. But we could also modify the flags so these specific tests run without --enable-unsafe-webgpu so we get the test coverage.