CiviEventDispatcher::dispatch() - add deprecation warning for deprecated event class

[demeritcowboy]

Overview

See #26276 and #26212

Before

No warning - extension will fail hard in drupal 10 or when civi ups the minimum symfony version.

After

Warning

Technical Details

See above linked PRs.

I've linked to the dev docs where we could add some more discussion so have tried to keep the message here straightforward and not require too much thinking for those who don't need it. See also https://lab.civicrm.org/documentation/docs/dev/-/merge_requests/1078 since the dev docs reference the outdated class.

Comments

I tested what happens if run when the class doesn't exist. It doesn't seem to mind.

@totten @dontub

[civibot]

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[totten]

Since just start 5.64.alpha, I think it's good time to merge this.

@demeritcowboy - I did some r-run on D7 (make a fake extension; have it fire some event-classes), and it seemed to work well. Warning appeared in both web UI and log.