fix(ext/node): validate handle type in child_process send() (#32711)
When `send(msg, handle)` is called with an invalid handle type (e.g. a
string), Node.js throws ERR_INVALID_HANDLE_TYPE. Deno was hitting a
generic `notImplemented()` error instead, since the handle validation
was missing before the not-implemented guard.
Now validates that the handle is a recognized type (net.Socket, Server,
or object with _handle) before rejecting, matching Node.js error
behavior.