RFR: 8340565: Create separate index page for terms defined by the index tag

[Hannes Wallnöfer]

On Wed, 9 Oct 2024 17:49:23 GMT, Hannes Wallnöfer <hannesw at openjdk.org> wrote:

> This change adds a conditional `search-tags.html` page to list all search tags defined by the `{@index ... }` tag. Since search tags work very similar to the `{@systemProperty ...}` tag and are internally represented by the same class I changed `SystemPropertiesWriter.java` into an abstract base class called `IndexItemListWriter.java`, with concrete subclasses for system properties and search tags.
> 
> JavaDoc also generates index items for documentation headings, these are not included in `search-tags.html`.
> 
> [This is the Search Tags page for JDK API docs](https://cr.openjdk.org/~hannesw/8340565/api.00/search-tags.html) (top-level files only).

Out of curiosity, I hacked up two writers that list search items derived from [`<h1>` tags][h1] and [`<h2>` tags][h2]. While  think these items are very valuable in search, the signal/noise ratio in listed form appears rather low even for those higher-level headings.

[h1]: https://cr.openjdk.org/~hannesw/8340565/api.hdr/h1-search-tags.html
[h2]: https://cr.openjdk.org/~hannesw/8340565/api.hdr/h2-search-tags.html

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PR Comment: https://git.openjdk.org/jdk/pull/21429#issuecomment-2404418295