node:worker_threads: implement postMessageToThread [1bx5ty] - #29828

Because `setupMainThreadPort` only runs when the worker first evaluates `node:worker_threads` (while the parent eagerly registers the port in `threadsPorts` during the `Worker` constructor), `postMessageToThread(thatWorkerId, value)` with no timeout will return a promise that never settles if the target worker's script never imports `worker_threads`. In Node the messaging port is wired during worker bootstrap, so the same call rejects promptly with `ERR_WORKER_MESSAGING_FAILED` instead of hangin

The `onmessageerror` setter (JSMessagePort.cpp:234) still calls `jsRef()`, which now sets `m_wantsExplicitRef = true` — so `port.onmessageerror = fn; port.hasRef()` returns `true` and the port refs the event loop, contrary to the resolved review thread's claim that this refactor makes Bun match Node (where it returns `false`). The header comment for `m_wantsExplicitRef` ("from .ref() or the onmessage setter") confirms `onmessageerror` was overlooked; the simplest fix is to drop the `jsRef()` cal