FieldAccessException in KeyFrame Setter when propery is in an external F# assembly

[marklam]

Describe the bug
A control defined in an F# class library cannot be animated because a FieldAccessException is raised.

System.FieldAccessException
  HResult=0x80131507
  Message=Attempt by method 'AvaloniaApplication1.MainWindow.!XamlIlPopulate(System.IServiceProvider, AvaloniaApplication1.MainWindow)' to access field 'ControlLibraryFS.StringFormatFloatTextBlock.ValueProperty' failed.
  Source=AvaloniaApplication1
  StackTrace:
   at AvaloniaApplication1.MainWindow.!XamlIlPopulate(IServiceProvider , MainWindow ) in C:\temp\AvaloniaReflectionProb\AvaloniaApplication1\AvaloniaApplication1\MainWindow.axaml:line 15
   at AvaloniaApplication1.MainWindow.!XamlIlPopulateTrampoline(MainWindow )
   at AvaloniaApplication1.MainWindow.InitializeComponent() in C:\temp\AvaloniaReflectionProb\AvaloniaApplication1\AvaloniaApplication1\MainWindow.axaml.cs:line 19
   at AvaloniaApplication1.MainWindow..ctor() in C:\temp\AvaloniaReflectionProb\AvaloniaApplication1\AvaloniaApplication1\MainWindow.axaml.cs:line 11
   at AvaloniaApplication1.App.OnFrameworkInitializationCompleted() in C:\temp\AvaloniaReflectionProb\AvaloniaApplication1\AvaloniaApplication1\App.axaml.cs:line 18
   at Avalonia.Controls.AppBuilderBase`1.Setup() in /_/src/Avalonia.Controls/AppBuilderBase.cs:line 313
   at Avalonia.Controls.AppBuilderBase`1.SetupWithLifetime(IApplicationLifetime lifetime) in /_/src/Avalonia.Controls/AppBuilderBase.cs:line 180
   at Avalonia.ClassicDesktopStyleApplicationLifetimeExtensions.StartWithClassicDesktopLifetime[T](T builder, String[] args, ShutdownMode shutdownMode) in /_/src/Avalonia.Controls/ApplicationLifetimes/ClassicDesktopStyleApplicationLifetime.cs:line 208
   at AvaloniaApplication1.Program.Main(String[] args) in C:\temp\AvaloniaReflectionProb\AvaloniaApplication1\AvaloniaApplication1\Program.cs:line 14

The control works correctly without animation.

A similar control defined in a C# assembly can be animated.

Also if the F# control is defined in the same assembly as the Avalonia App, then the animation works (obviously this requires an F# Avalonia App project).

To Reproduce
There is a repo with a C# app and the C# and F# versions of the control here

Running the app with the xaml as-is will attempt to animate the C# and F# controls. Commenting-out the animation style for the control in the cf namespace shows that the F# control works ok otherwise, and the C# version can animate.

Expected behavior
The F# control to behave the same way as the C# control under the animation.

Desktop (please complete the following information):

• OS: Windows 10
• Version 0.10.12

Additional context
Decompiling the F# assembly to C# in ILSpy shows that the main difference is that the property definitions are:

	public static readonly StyledProperty<string> StringFormatProperty;
	public static readonly StyledProperty<double> ValueProperty;

in C#, but in F# they are:

	internal static StyledProperty<string> StringFormatProperty;
	internal static StyledProperty<double> ValueProperty;

Presumably this is handled OK by the setter used for

    <cf:StringFormatFloatTextBlock Value=".98" StringFormat="{}{0:00.00%}" />

but not for

    <Style Selector="cf|StringFormatFloatTextBlock">
      <Style.Animations>
        <Animation Delay="0:0:2" Duration="0:0:30" IterationCount="1" FillMode="Both">
          <KeyFrame Cue="0%">
            <Setter Property="Value" Value ="0"/>
          </KeyFrame>
          <KeyFrame Cue="100%">
            <Setter Property="Value" Value ="1"/>
          </KeyFrame>
        </Animation>
      </Style.Animations>
    </Style>