Have Generic Symfony event dispatcher in core

[sharidas]

It would be nice to have a generic symfony event dispatcher in core. Currently there are multiple places where we have used symfony event dispatcher which can be moved to a generic class to handle the event dispatchers.

[ownclouders]

GitMate.io thinks possibly related issues are #30054 ([stable10] Bump symfony/event-dispatcher from 3.2.4 to 3.2.14), #29651 ([WIP] Add new symfony dispatcher events), #29174 (Provide symfony event dispatcher events for all older hook types), #30996 (Throw symfony events on group actions), and #31138 (Unified symfony event for updates happening in share).