Vendor more recent node version?

Emsdk includes node v14.18 which is quite old. In particular, one annoying thing about it is that it requires the `--experimental-wasm-bigint` flag which is poorly documented (it doesn't appear in `node --help`) and future versions of node error out if passed `--experimental-wasm-bigint` so it's pretty hard to handle new and old nodes. Also, the error message `wasm function signature contains illegal type` has nothing that suggests it has anything to do with `-sWASM_BIGINT` or with `--experimental-wasm-bigint` or anything. This is wasting a fair amount of time for various people who are seeing this bug and having to investigate. I think it would help a lot to vendor a newer version, say v16.15 LTS.