Ship an Intl-enabled engine #362

The shipped engines are built with --without-intl-api, so /\p{L}/u is a parse-time SyntaxError, and String.prototype.normalize and Intl are missing.

StarlingMonkey #368 (refs #45) adds an opt-in ENABLE_INTL CMake option, with prebuilt release_intl / release_weval_intl SpiderMonkey tarballs. An engine built with it works today through --engine. It is ~32 MB vs ~10.5 MB, mostly ICU data.

Once a StarlingMonkey release includes #368:

• build starlingmonkey_embedding_intl.wasm (+ a weval variant)
• add enableIntl (default false) to pick it, and --intl in jco

Happy to send the PR