RFR: 8306021: Add event handler management to EventTarget [v4]

[Marius Hanl]

On Mon, 17 Apr 2023 06:00:19 GMT, Michael Strauß <mstrauss at openjdk.org> wrote:

>> This PR adds the following methods to the `EventTarget` interface:
>> 1. `addEventHandler`
>> 2. `removeEventHandler`
>> 3. `addEventFilter`
>> 4. `removeEventFilter`
>
> Michael Strauß has updated the pull request incrementally with one additional commit since the last revision:
> 
>   doc changes

LGTM

-------------

Marked as reviewed by mhanl (Committer).

PR Review: https://git.openjdk.org/jfx/pull/1090#pullrequestreview-1421893416