update projects to .NET 5 (Win7) & update OpenTK to latest Version to support .NET 5 (missing OpenTK.GLControl)

Pilz.Drawing.Drawing3D.OpenGLRenderer/Pilz.Drawing.Drawing3D.OpenGLFactory.vbproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <MyType>Windows</MyType>
-    <TargetFramework>net48</TargetFramework>
+    <TargetFramework>net5.0-windows7.0</TargetFramework>
     <NoWarn>42016,41999,42017,42018,42019,42032,42036,42020,42021,42022</NoWarn>
     <DocumentationFile>Pilz.Drawing.Drawing3D.OpenGLFactory.xml</DocumentationFile>
     <DefineTrace>true</DefineTrace>
@@ -29,14 +29,10 @@
     <PackageReference Include="System.Net.Http" Version="4.3.4" />
   </ItemGroup>
   <ItemGroup>
-    <PackageReference Include="OpenTK" Version="3.2" />
+    <PackageReference Include="OpenTK" Version="4.2.0" />
     <PackageReference Include="OpenTK.GLControl" Version="3.1.0" />
     <PackageReference Include="System.Numerics.Vectors" Version="4.5.0" />
   </ItemGroup>
-  <ItemGroup>
-    <Reference Include="Microsoft.VisualBasic" />
-    <Reference Include="System.Windows.Forms" />
-  </ItemGroup>
   <ItemGroup>
     <Import Include="Microsoft.VisualBasic" />
     <Import Include="System" />
@@ -52,9 +48,7 @@
     <Compile Update="Preview\ModelPreview.Designer.vb">
       <DependentUpon>ModelPreview.vb</DependentUpon>
     </Compile>
-    <Compile Update="Preview\ModelPreview.vb">
-      <SubType>Form</SubType>
-    </Compile>
+    <Compile Update="Preview\ModelPreview.vb" />
     <Compile Update="My Project\Application.Designer.vb">
       <AutoGen>True</AutoGen>
       <DependentUpon>Application.myapp</DependentUpon>