feat: MessagePorts in the main process (#22404)

docs/api/message-port-main.md

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+# MessagePortMain
+
+`MessagePortMain` is the main-process-side equivalent of the DOM
+[`MessagePort`][] object. It behaves similarly to the DOM version, with the
+exception that it uses the Node.js `EventEmitter` event system, instead of the
+DOM `EventTarget` system. This means you should use `port.on('message', ...)`
+to listen for events, instead of `port.onmessage = ...` or
+`port.addEventListener('message', ...)`
+
+See the [Channel Messaging API][] documentation for more information on using
+channel messaging.
+
+`MessagePortMain` is an [EventEmitter][event-emitter].
+
+## Class: MessagePortMain
+
+### Instance Methods
+
+#### `port.postMessage(message, [transfer])`
+
+* `message` any
+* `transfer` MessagePortMain[] (optional)
+
+Sends a message from the port, and optionally, transfers ownership of objects
+to other browsing contexts.
+
+#### `port.start()`
+
+Starts the sending of messages queued on the port. Messages will be queued
+until this method is called.
+
+#### `port.close()`
+
+Disconnects the port, so it is no longer active.
+
+### Instance Events
+
+#### Event: 'message'
+
+Returns:
+
+* `messageEvent` Object
+  * `data` any
+  * `ports` MessagePortMain[]
+
+Emitted when a MessagePortMain object receives a message.
+
+[`MessagePort`]: https://developer.mozilla.org/en-US/docs/Web/API/MessagePort
+[Channel Messaging API]: https://developer.mozilla.org/en-US/docs/Web/API/Channel_Messaging_API