RFR: 8346109: Create JDK taglet for additional preview notes

[Roger Riggs]

On Fri, 31 Jan 2025 16:19:17 GMT, Hannes Wallnöfer <hannesw at openjdk.org> wrote:

> Please review a patch to add a JavaDoc Taglet to the JDK build system that allows to add preview-related notes to non-preview API elements, as well as a hidden javadoc option to add elements with preview notes to the preview summary page.
> 
> The {@previewNote} tag uses the following syntax:
> 
> 
> {@previewNote <jep-number> [preview note title]}
> preview note text
> {@previewNote}
> ``` 
> 
> Elements with preview notes are listed in a separate table titled "Elements containing Preview Notes" in the preview summary page. 
> 
> To support the feature, the algorithm in `PreviewAPIListBuilder.java` was changed to retrieve the preview JEP info in advance before looping through API elements. While this is not strictly necessary, it makes the code a bit nicer, and it also allows us to avoid checking for preview API elements when processing non-JDK code.

Yuck.  It would, IMHO, look better if it was a BOLD prefix of the first sentence. i.e.

**Preview Feature:** Checks that the specified object reference is an identity object.

$.02

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PR Comment: https://git.openjdk.org/jdk/pull/23395#issuecomment-2790517937