Replace SceneForm, which has been discontinued

[kamszyc]

I noticed that ARToolkit for Android uses quite old versions of ARCore and Sceneform libraries.
There had been an attempt to update them, but they have been downgraded to 1.11.0 in commit: 18fc3a7.

What's the reasoning behind this decision?
Updating dependencies to newest versions should be beneficial to the project.

Furthermore, Sceneform got discontinued by Google
https://github.com/google-ar/sceneform-android-sdk/blob/master/README.md.
ARToolkit should switch to maintained Sceneform fork by Thomas Gorisse or some other solution
https://github.com/ThomasGorisse/sceneform-android-sdk.

I created an issue asking for updating Xamarin.Android binding to use the fork
xamarin/XamarinComponents#1268.

[mbranscomb]

@dotMorten @nCastle1

[nCastle1]

The AR Toolkit has been updated to reference the most recent versions of SceneForm and ARCore that are available through Xamarin packages. The updated packages solved some problems but caused others. The most recent release (100.13) of AR Toolkit solves or works around all of the problems found through testing.

We have not yet decided on the long-term solution to the discontinuation of SceneForm. This issue affects the native Android/Kotlin version of the AR Toolkit for Android. We'll need to make sure both .NET and native Android maintain feature and performance parity for whatever solution we choose.

This issue can stay open to track the work of finding a SceneForm replacement.