Add uncapturederror test

[greggman]

It wasn't clear if I should just put this test in error_scope.spec.ts or put it here where there was a TODO but technically this isn't error scope so ?

Also the constructor is tested in src/webgpu/idl/constructable.spec.ts

This came up because I was working on the webgpu-debug-helper and needed to test some stuff.

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Requirements for PR author:

• [X] All missing test coverage is tracked with "TODO" or .unimplemented().
• [X] New helpers are /** documented */ and new helper files are found in helper_index.txt.
• [X] Test behaves as expected in a WebGPU implementation. (If not passing, explain above.)
• [X] Test have be tested with compatibility mode validation enabled and behave as expected. (If not passing, explain above.)

Requirements for reviewer sign-off:

• [ ] Tests are properly located in the test tree.
• [ ] Test descriptions allow a reader to "read only the test plans and evaluate coverage completeness", and accurately reflect the test code.
• [ ] Tests provide complete coverage (including validation control cases). Missing coverage MUST be covered by TODOs.
• [ ] Helpers and types promote readability and maintainability.

When landing this PR, be sure to make any necessary issue status updates.

[kainino0x]

It wasn't clear if I should just put this test in error_scope.spec.ts or put it here where there was a TODO but technically this isn't error scope so ?

This seems fine, no strong feeling whether it should be in error_scope or not. Kinda ambiguous because it's part of the same system, sort of like the "catch-all" error scope, but since there might end up being other uncapturederror tests in this file someday, separate file makes enough sense.

[greggman]

LGTM but I think you forgot to upload src/webgpu/idl/constructable.spec.ts

src/webgpu/idl/constructable.spec.ts already exists and already has a test that creates each error type and a GPUUncapturedErrorEvent

[greggman]

https://github.com/gpuweb/cts/blob/441db0a23175268d4a49310a9b4d2f0e3c15dc62/src/webgpu/idl/constructable.spec.ts#L48

[kainino0x]

Oh, sorry, got it. LGTM then!