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

[Andy Goryachev]

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 just wanted to mention a bit of asymmetry between the way header bars are added to the `Stage` vs. `Dialog`.  Probably nothing we could do here, and `DialogPane` property is the right approach.

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PR Comment: https://git.openjdk.org/jfx/pull/1943#issuecomment-3499899614