(NFC) CiviEventDispatcher - Update type declaration. Add test demonstion

[totten]

Overview

This is a revision of @dontub's #26212. (cc @demeritcowboy)

Before

dispatcher($eventName, $event) hints that the $event is type Event. This does not resolve to a valid class. (\Civi\Core\Event does not exist.)

After

dispatcher($eventName, $event) hints that the $event is type object.

Technical Details

• It already works, as you can see in the unit-test. This is because we've inherited behavior from Symfony 4.4+ (which supports PSR-14).
• PSR-14 recommends modeling events as any kind of object.
• There's currently no need for Civi to specifically have a PSR-14 adapter or integration. But this doesn't hurt us either.
• https://en.wikipedia.org/wiki/Robustness_principle

[civibot]

(Standard links)

• If you are reviewing this pull-request, you may wish to consult the test sites and the Review Standards (long template, short template).

[demeritcowboy]

The main reason for encouraging GenericHookEvent (or at least something civi controls) is so that extension authors can be insulated from whatever symfony/drupal/php does next, and given the above links there's a wide range of things they could do. By using whatever object Civi is using, they know their code will be compatible across supported versions. Of course civi could change what it uses too, but it would least make an attempt to stay compatible.

It can dochint object, but then it's up to authors to keep up with whatever they need to do to be cross-compatible. So I'm still wondering if it should more strongly suggest using GenericHookEvent, although I do understand the comments in the other PR that that class might include stuff that isn't wanted.

For what it's worth object (currently) works on drupal 10/symfony 6 too.

[totten]

@demeritcowboy - Yeah, the cross-compatibility is an important consideration. I took another stab at the description.

[demeritcowboy]

Have put merge-ready in case @dontub has any comments.

And can think about this after but a followup might be to add a deprecation warning to dispatch() if someone is passing in a Symfony\Component\EventDispatcher\Event (as opposed to \Symfony\Contracts\EventDispatcher\Event), because that isn't forward-compatible with symfony 6. A quick look at universe I see at least one.

[totten]

OK, so no more comments. And it's NFC. Merging.

(@demeritcowboy) ...a followup might be to add a deprecation warning to dispatch() if someone is passing in a Symfony\Component\EventDispatcher\Event...

Oof, yeah, I found ~12 extensions in my copy of universe. Probably a good idea.