Switch to .NET6 for WPF

samples/WpfSamplesHost/WpfSamplesHost.csproj

@@ -2,7 +2,8 @@
 
   <PropertyGroup>
     <OutputType>WinExe</OutputType>
-    <TargetFramework>netcoreapp3.1</TargetFramework>
+	<TargetFramework>net6.0-windows</TargetFramework>
+	<Nullable>enable</Nullable>
     <UseWPF>true</UseWPF>
   </PropertyGroup>
 

src/StandardUI.VisualEnvironment.WpfNative/StandardUI.VisualEnvironment.WpfNative.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk.WindowsDesktop">
 
 	<PropertyGroup>
-		<TargetFrameworks>netcoreapp3.1;net472</TargetFrameworks>
+		<TargetFrameworks>net6.0-windows;net472</TargetFrameworks>
 		<UseWPF>true</UseWPF>
 		<LangVersion>8.0</LangVersion>
 		<Nullable>enable</Nullable>