fix: do not crash the event emitting parent process if on listener fails

[SebastianKrupinski]

Resolves

Currently when a miss behaving event listener errors with out proper error catching this causes the emitting process to error also.

The issue here is that at this causes data loss and loss of functionality in unrelated apps. For instance, when saving a Calendar Appointment we emit a create calendar object event for every attendee that the event is saved to.

E.g.
Attendee 1 (Save Object) -> Emit Event ->Attendee 2 (Save Object) -> Emit Event -> Organizer (Save Object) -> Emit Event

So when a event listener errors after the first emit the entire process crashes and we lose data, even though the emitting process experienced no errors. As event listeners can be implemented by any app, there is no way to make sure that the code being executes is safe.

Some example of recent issues that causes user confusion and data loss..

Constructor errors

TypeError: OCA\Talk\Listener\CalDavEventListener::__construct(): Argument #6 ($userId) must be of type string, null given
#26 /spreed/lib/Listener/CalDavEventListener.php(32): OCA\Talk\Listener\CalDavEventListener::__construct

Runtime errors

ErrorException: Warning: Attempt to read property "LOCATION" on null
#17 /spreed/lib/Listener/CalDavEventListener.php(68): OCA\Talk\Listener\CalDavEventListener::handle

Summary

• extends the symfony event dispatcher to catch errors in event listeners, to prevent the emitting process crashing in the event that a event listener errors without handling the exception

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[ChristophWurst]

PSR includes error handling and unfortunately catching listener errors would "break" the standard: https://www.php-fig.org/psr/psr-14/#error-handling

[SebastianKrupinski]

Yeah, I figured this might not fly.