[2.3][EventDispatcher] Make events lighter

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | yes
| Tests pass?   | yes
| Fixed tickets | na
| License       | MIT
| Doc PR        | symfony/symfony-docs#2476

I've taken the previous discussions and taking into consideration @fabpot does not want to break BC. This PR now provides the `EventDispatcher` as an argument to listeners. I've made a second separate commit which also passes the event name.

This PR is alternative to #7582