contentBuilder property
Builder for the popover content.
Receives a close callback so content can dismiss the popover
programmatically (e.g., a "Done" button).
The content is rendered directly inside the morphing GlassContainer, so it inherits the glass effect. The widget should use MainAxisSize.min or constrained height to size correctly.
Implementation
final Widget Function(BuildContext context, VoidCallback close)
contentBuilder;