RFR: 8370446: Support dialogs with StageStyle.EXTENDED [v2]

[Michael Strauß]

On Fri, 31 Oct 2025 00:07:46 GMT, Michael Strauß <mstrauss at openjdk.org> wrote:

>> Adds the `DialogPane.headerBar` property, which allows developers to specify a custom `HeaderBar` when the dialog uses the `EXTENDED` stage style.
>
> Michael Strauß has updated the pull request incrementally with one additional commit since the last revision:
> 
>   move HeaderBar to DialogPane

I've moved the new API from `Dialog` (which roughly corresponds to a `Stage`) to `DialogPane`, which contains the scene graph of a dialog. All bugs you've found should also be fixed.

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PR Comment: https://git.openjdk.org/jfx/pull/1943#issuecomment-3470867748