RFR: JDK-8312058: Documentation improvements for subscription based listeners [v6]

[Andy Goryachev]

On Fri, 11 Aug 2023 22:03:28 GMT, John Hendrikx <jhendrikx at openjdk.org> wrote:

>> Incorporates documentation review comments from #1069.
>> 
>> This PR should be kept minimal so it can be backported to JFX21; it should only contain documentation changes.
>
> John Hendrikx has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Update wording on value subscriber

changes since last review look good.

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Marked as reviewed by angorya (Reviewer).

PR Review: https://git.openjdk.org/jfx/pull/1177#pullrequestreview-1577003625