RFR: JDK-8304439: Subscription based listeners [v7]

[Johan Vos]

On Sun, 2 Jul 2023 11:46:19 GMT, John Hendrikx <jhendrikx at openjdk.org> wrote:

>> Makes `Subscription` public (removing some of its methods that are unnecessary), and adds methods that can provide `Subscription`s in `ObservableValue`.
>
> John Hendrikx has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Add newline at end of ConditionalBinding file

I believe this is a valuable addition that will take away one of the major pain points for developers (having to keep a reference to the passed lambda, as explained in the JBS issue).
I did read the comments and discussion, and it seems everything is addressed. I don't have naming preferences, so I'm fine with the suggested ones.
I looked at the code and ran the tests, all good. 
I don't see performance implications in existing code, and I didn't spot potential performance issues using the subscription-based approach.

I believe this change will lead to questions about "best patterns" from developers. I don't think we need lots of discussion about this in the code/javadoc, although some components in the OpenJFX codebase do so.

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PR Comment: https://git.openjdk.org/jfx/pull/1069#issuecomment-1627651103