doc: add class worker documentation

Add documentation about Worker class inherits from EventEmitter.

PR-URL: #24849
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>

Author: yoshimoto8

doc/api/worker_threads.md

@@ -234,6 +234,8 @@ listeners for the event exist.
 added: v10.5.0
 -->
 
+* Extends: {EventEmitter}
+
 The `Worker` class represents an independent JavaScript execution thread.
 Most Node.js APIs are available inside of it.