[DO NOT MERGE] Include Adorners in matrix calculations in VisualExtensions

[BAndysc]

What does the pull request do?

This PR changes VisualExtensions::TransformToVisual to support adorners.

What is the current behavior?

Currently VisualExtensions::TransformToVisual doesn't work correctly when one of the controls is inside an Adorner Layer. Adorned element is not on a path to root from adorner element. So it is not included in calculations. Adorners are rendered correctly, because the renderer has special handling for adorners. Hence TransformToVisual needs some special handling too.

What is the updated/expected behavior with this PR?

VisualExtensions::TransformToVisual should correctly take into account adorners.

How was the solution implemented (if it's not obvious)?

Unfortunately, adorners are defined in Avalonia.Controls while VisualExtensions is in Avalonia.Base, so VisualExtensions doesn't know what adorners are. Therefore, this PR adds AdornerLayerBase with AdornedElementProperty and an empty IAdornerLayer to Avalonia.Base so that this information is available. This is far from perfect, but I don't know how to do it in a cleaner way.

Besides, the obvious downside of the solution is additional computation complexity in VisualExtensions::TransformToVisual. Each time this method is called, an adorned element needs to be found via calling GetValue(AdornedElementProperty) on each element on path to root.

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

Obsoletions / Deprecations

Fixed issues

Fixes #15480

[avaloniaui-bot]

You can test this PR using the following package version. 11.2.999-cibuild0047604-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[maxkatz6]

As per @kekekeks, whole situation with "adorner transformation processed on composition thread" should be changed to be done on UI thread. So, I am not sure how we should process with this PR (and previous already merged).

[BAndysc]

I understand. However, until it is properly fixed, I would appreciate if this PR could remain open, as I use adorners a lot in my app (and it worked fine in Avalonia 0.10), thus for now I can use nightly builds produced by this PR.

[avaloniaui-bot]

You can test this PR using the following package version. 11.2.999-cibuild0047725-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[timunie]

@BAndysc we can leave it open, but I'd like to mark it as draft and won't merged for now, just in case

[avaloniaui-bot]

You can test this PR using the following package version. 11.2.999-cibuild0048166-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]