Real DNS resolution for getaddrinfo under -sNODERAWSOCKETS

[guybedford]

This gives getaddrinfo() real name resolution under -sNODERAWSOCKETS. Split out from #27182, which also added a new asynchronous DNS API; this PR is only the change to the existing blocking API, allowing any async API work to follow separately.

Previously every hostname resolved to a fake 172.29.x.x address, which is fine for the websocket proxy transport but not for real Node.js sockets, where the address has to be connectable.

• /etc/hosts entries (read fresh through the emscripten FS, so MEMFS or a mounted file works) resolve synchronously.
• Any other hostname resolves via node:dns. The lookup is asynchronous, so getaddrinfo blocks by returning a Promise where the calling stack can wait on it: a sync-proxied pthread (PROXY_SYNC_ASYNC, e.g. main() under PROXY_TO_PTHREAD), or ASYNCIFY/JSPI by suspending. Numeric and /etc/hosts results still return synchronously, so JSPI does not pay a microtask on those.
• Where there is no stack that can wait (the event-loop thread itself), a hostname needing DNS returns EAI_AGAIN.
• Results may now be an addrinfo linked list (multiple /etc/hosts entries, multiple DNS records, AF_UNSPEC), and freeaddrinfo walks the whole chain.

Everything is gated on NODERAWSOCKETS; without it getaddrinfo is unchanged.

Implementation-wise the existing body becomes $doGetAddrInfo, which returns either an EAI_* code or a thunk producing a Promise of one, and getaddrinfo is a thin dispatcher on that. The thunk form keeps the ASYNCIFY rewind re-invocation from starting a second lookup.

Tested with test_noderawsockets_dns (numeric, /etc/hosts aliases and multi-address lists across families, EAI_AGAIN single-threaded), test_noderawsockets_dns_blocking under PROXY_TO_PTHREAD and test_noderawsockets_dns_blocking_jspi, plus ASYNCIFY and ASYNCIFY + PROXY_TO_PTHREAD manually.

Made with AI assistance under my review