Add lint to ensure kKnownWGSLLanguageFeatures is complete

[kainino0x]

This is to prevent tests from being written against WGSL language features without adding them to kKnownWGSLLanguageFeatures so that they will be tested by the wgsl_matches_api test.

It's not 100% foolproof, but should work pretty well. Best I think we can do without updating eslint and installing an extra dep to allow the eslint config to be written in TypeScript so it can import the same list that we use in the CTS.

Tested locally, the lint fails if I take any of the items out of the new list.

Issue: https://crbug.com/557328524

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Requirements for PR author:

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

Requirements for reviewer sign-off:

• [n/a] Tests are properly located.
• [n/a] Test descriptions are accurate and complete.
• [n/a] Tests provide complete coverage (including validation control cases). Missing coverage MUST be covered by TODOs.
• [n/a] Tests avoid over-parameterization (see case count report).

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

[github-actions]

Results for build job (at ad6f6ad):

 Test case/subcase counts did not change.