avalonia: Update Avalonia sample to target Avalonia 12

Author: mfkl

samples/LibVLCSharp.Avalonia.Sample/LibVLCSharp.Avalonia.Sample.csproj

@@ -15,8 +15,8 @@
     <AvaloniaResource Include="Assets\**" />
   </ItemGroup>
   <ItemGroup>
-    <PackageReference Include="Avalonia.Desktop" Version="11.3.13" />
-    <PackageReference Include="Avalonia.Themes.Fluent" Version="11.3.13" />
+    <PackageReference Include="Avalonia.Desktop" Version="12.0.0" />
+    <PackageReference Include="Avalonia.Themes.Fluent" Version="12.0.0" />
   </ItemGroup>
   <ItemGroup>
     <PackageReference Condition="$([MSBuild]::IsOsPlatform('Windows'))" Include="VideoLAN.LibVLC.Windows" Version="3.0.21" />

samples/LibVLCSharp.Avalonia.Sample/Views/VideoPlayer.axaml

@@ -6,6 +6,7 @@
              xmlns:viewModels="clr-namespace:LibVLCSharp.Avalonia.Sample.ViewModels"
              mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
              x:Class="LibVLCSharp.Avalonia.Sample.Views.VideoPlayer"
+             x:DataType="viewModels:MainWindowViewModel"
              DataContextChanged="OnDataContextChanged">
 
     <Design.DataContext>