provide @types/llrt .d.ts files for built in modules

[everett1992]

Expressing the Node.js compatibility matrix and API guide as typescript .d.ts files would let users statically check that they are only using supported features, and provide inline IDE documentation.

Users could rely on @types/node but would have to guess at the target version (is it 20, 18, 22?) and remember which APIs aren't supported or rely on tests.

[richarddavison]

That's a great idea! Thanks for the suggestion