[AncestorBinding] add option to support crawling across popup/flyout+host boundary

[Xiaoy312]

What would you like to be added:

<Button>
	<Button.Flyout>
		<Flyout>
			<Button DataContext="{utu:AncestorBinding AncestorType=Button, Path=DataContext...}" />

Why is this needed:

When materialized, the inner button is under the popup branch separate from the outer button's causing the crawling to fail.

For which Platform: all

Anything else we need to know?

Can we even trace back the associated host from the flyout/popup itself?
unoplatform/Uno.Samples#681

[Xiaoy312]

uno: [Popup.AssociatedFlyout].Target can be used to retrieve the host // bracket denotes [internal property]
win: impossible to do without doing a full crawling of visual tree, and comparing every flyout-host's flyout's content to the FlyoutPresenter's content... and, we have multiple "flyout" MenuFlyout, Tooltip, etc.

[agneszitte]

@kazo0, @Xiaoy312 what would be the priority of this issue please

[Xiaoy312]

no idea, just a nice-to-have feature, not really requested by any entity... just not yet
also, i dont really see a reasonable way to achieve this for windows atm...
so it is kinda blocked