RFR: 8370446: Support dialogs with StageStyle.EXTENDED

[Andy Goryachev]

On Tue, 21 Oct 2025 23:54:55 GMT, Michael Strauß <mstrauss at openjdk.org> wrote:

> Adds the `Dialog.headerBar` property, which allows developers to specify a custom `HeaderBar` when the dialog uses the `EXTENDED` stage style. The property is ignored for all other stage styles.

modules/javafx.controls/src/main/java/javafx/scene/control/Dialog.java line 593:

> 591:      * @since 26
> 592:      */
> 593:     private final ObjectProperty<HeaderBar> headerBar = new SimpleObjectProperty<>(this, "headerBar") {

This property should be lazily initialized (I know it's just a draft POC)

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PR Review Comment: https://git.openjdk.org/jfx/pull/1943#discussion_r2452488407