Symfony version(s) affected: >=4.3.0

Description
When using workflow as standalone component it will not work when in production due to missing dependency on symfony/event-dispatcher

How to reproduce

composer.json

{
    "require": {
        "symfony/workflow": "4.3"
    }
}

test.php

use Symfony\Component\Workflow\Definition;
use Symfony\Component\Workflow\Workflow;

include 'vendor/autoload.php';

$workflow = new Workflow(new Definition(['a'], []));

Run composer without dev dependencies
composer install --no-dev

Running test.php will result in

PHP Fatal error:  Uncaught Error: Class 'Symfony\Component\EventDispatcher\LegacyEventDispatcherProxy' not found in ...

Possible Solution

Either do a null check before trying to call LegacyEventDispatcherProxy::decorate or add symfony/event-dispatcher as a required dependency.