Add tests for workers-types that run in CI

[Cherry]

Over the last year or so, there have been regular regressions or issues with workers-types that would have been caught with some testing and/or better vetting.

workers-types is a huge cornerstone in the Cloudflare Workers development experience, with TypeScript being the recommended language across the docs, npm create cloudflare, etc. It would be really good to see this have a much more first-class experience and release/vetting process.

Examples:

• types: Response is no longer compatible with ResponseInit #2765
• Unexpected change in DOMException.stack type #2174
• URL getters (etc.) now returning ArrayBufferView and not string #1818
• Unexpected change in R2Checksums types #2211
• Minor regression in types params names with 4.20240903.0 #2652

There do appear to be some tests created in https://github.com/cloudflare/workerd/tree/main/types/test, but I'm not sure how often these run, or if they run in CI, or how much coverage they provide? It would be really nice if these ran regularly and perhaps even a diff of types changes were added into PRs so the types output can be analysed quickly and easily.

[penalosa]

This is a great callout. The types tests do run in CI, but they're more about testing the type generation logic rather than making sure the published types are what people expect. I think having a snapshot test of the type generation would be a great improvement, so the changes to the published types could be reviewed in PRs.