[maxkatz6]

What does the pull request do?

This PR adds new API to access Popups opened on the specific TopLevel target.

public class TopLevel
{
+    IReadOnlyList<Popup> OpenedPopups { get; }
}
public class Popup
{
+    IReadOnlyList<Popup> OpenedPopups { get; }
}

public class static HeadlessWindowExtensions
{
-    public static IReadOnlyList<TopLevel> GetOpenPopups(this TopLevel topLevel);
}

Important implementation details to mention:

1. Property returned a new collection on each call, similarly to Window.OwnedWindows property.
2. Returned value doesn't implement INCC, instead Popup.IsOpenProperty callbacks are recommended.
3. This API returns list of Popup, unlikely removed API from #21889 that returned list of top levels. List of top levels is not applicable with overlay popups, and it's generally confusing to get TopLevel when you ask for Popups. But at the same time Popup is a bit less useful in headless testing, so it now requires an extra helper to resolve top level from a popup (if present).

Checklist

• Added unit tests (if possible)?
• Added XML documentation to any related classes?
• Consider submitting a PR to https://github.com/AvaloniaUI/avalonia-docs with user documentation

Breaking changes

Breaking change between nightly builds - removed API.

Fixed issues

Fixes #8403
And replaces new API from #21889

[robloo]

How does this take into account Flyouts?

[maxkatz6]

@robloo current flyouts are implemented with Popups, as well as ToolTips. This new API will return backing popups for both of them.

[avaloniaui-bot]

You can test this PR using the following package version. 12.2.999-cibuild0068940-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]