Implement AsMessageHandler attribute

@lussoluca have you made progress?

No progress so far, freeing up in case it becomes to top of queue.

• Passes PHPStan (does not introduce new failures)
• Passes PHPCS
• Coverage for features (first tests for project!)
• Feature complete
• This work is already isolated from the mega-MR @ !MR2 so it may be committed as-is.
• Technique partially borrowed from Hux, the differences primarily being registerAttributeForAutoconfiguration is also used. See also reference https://symfony.com/blog/new-in-symfony-5-3-service-autoconfiguration-an...

Thanks @dpi!

RTBC for me

Restoring

Merged!

Addressing MessageHandlerInterface from issue summary: this issue does not implement this deprecated interface, instead message handlers can be implemented with Attributes on class or method or as a service.

Automatically closed - issue fixed for 2 weeks with no activity.