Add Origin Trial token for Subgroups in localhost:8080

[dneto0]

Adds a localhost:8080 token to standalone/index.html for local testing.

https://crbug.com/358117283

Followup to #3895

Issue: #

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Requirements for PR author:

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

Previously we've served up the localhost tokens from dev_server.ts instead. Do you need this because you're running this through some other server on localhost?

If so, I think it's redundant to have it in both, so we could have it only here and not in dev_server.ts.

[kainino0x]

Realized that other servers are supposed to work when building to disk (out/ directory) so it makes sense to support localhost:8080 on those.

We can remove the token from dev_server.ts (though it's not critical). If you do, update the comment below