RFR: 8349373: Support JavaFX preview features [v3]

[Kevin Rushforth]

On Fri, 7 Feb 2025 09:16:54 GMT, Michael Strauß <mstrauss at openjdk.org> wrote:

>> This PR contains a definition of preview features for JavaFX, as well as a helper class to verify that an application has opted into preview features.
>
> Michael Strauß has updated the pull request incrementally with four additional commits since the last revision:
> 
>  - javadoc
>  - remove supporting documentation
>  - warning can't be suppressed
>  - initialize PreviewFeature early

Looks good. I tested it and it does what I expected. I did some testing with the JDK and I was wrong about one thing:

> I don't think the warning should be suppressible; the equivalent JDK warning isn't

The key difference between the JDK and JavaFX is that the JDK only produces warnings (which are not suppressible) at compile time. Because of the compiler and JVM support, they didn't feel the need for a runtime warning.

Given that ours is a runtime warning, it might be worth restoring the system property to allow the warnings to be suppressed at runtime (default is false). What do you think?

Regarding compile time warnings for deprecated API: Should we specify that the `@Deprecated` annotation on preview features be marked as `forRemoval=true`? I can see arguments for both choices.

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Marked as reviewed by kcr (Lead).

PR Review: https://git.openjdk.org/jfx/pull/1359#pullrequestreview-2678498489