Enable event dispatcher in workers

[DenysKuchma]

Enable event dispatcher in workers

This allows plugins (e.g., Testomatio reporter) to receive events from workers
by emitting events through both this.emit() and event.dispatcher.emit().

Changes:

• lib/workers.js: Add event.dispatcher.emit() for all test/step/hook events
• lib/step/base.js: Add code field to Step.simplify() with serialized toCode() result
• lib/listener/globalTimeout.js: Use step.code field instead of calling toCode() method