Avalonia 12 support

[SKProCH]

Fix #501

I've removing the TreeDataGrid support, since its now a paid control. @klorman, sorry, but I don't have time to update it to some fork (and I don't know which one), so i'm accepting PRs to return it back

[SKProCH]

It still pretty much basic support, to make at least runnable.

[chen1tian]

Android system has some issues when using Combox、Button.Flyout etc.

android.runtime.JavaProxyThrowable: [System.InvalidOperationException]: Unable to create IPopupImpl and no overlay layer is found for the target control
                                                                                                    	at Avalonia.Controls.Primitives.OverlayPopupHost.CreatePopupHost + 0x3d(Unknown Source)
                                                                                                    	at Avalonia.Controls.Primitives.Popup.Open + 0x3f(Unknown Source)
                                                                                                    	at Avalonia.Controls.Primitives.Popup.IsOpenChanged + 0x18(Unknown Source)
                                                                                                    	at Avalonia.Controls.Primitives.Popup+<>c.<.cctor>b__25_1 + 0x0(Unknown Source)

[SKProCH]

Please, create a separate issue for that