title: Interactive window support for multiple runtimes .NET Core in vsix template
body: <p>In creating a template for VSIX we can allow the user to choose the .Net framework version
  This is how it is done:</p>
  <pre><code>&lt;TargetFrameworkVersion&gt;v$targetframeworkversion$&lt;/TargetFrameworkVersion&gt;
  </code></pre>
  <p>Now, with the release of the new version of Visual Studio (16.8), This allows the user to select the .NET Core version as well.
  But this code does not seem to work in the .NET Core template project and shows different numbers instead of netcoreapp3.1 or net50-windows values.
  also .net core use <code>&lt;TargetFramework&gt;</code> instead of <code>&lt;TargetFrameworkVersion&gt;</code>
  so What is the correct parameter?
  I tested these:</p>
  <p>1.result = 4.5</p>
  <pre><code>&lt;TargetFrameworkVersion&gt;$targetframeworkversion$&lt;/TargetFrameworkVersion&gt;
  </code></pre>
  <p>2.result = $targetframework$</p>
  <pre><code>&lt;TargetFramework&gt;$targetframework$&lt;/TargetFramework&gt;
  </code></pre>
  <p>3.result = 4.5</p>
  <pre><code>&lt;TargetFramework&gt;$targetframeworkversion$&lt;/TargetFramework&gt;
  </code></pre>