This helper doesn't solve our problems, but it's there.

  1. Make TerminalAppLib _not_ build App.xaml. I moved it to
     TerminalApp.vcxproj, so only the DLL builds it. No idea if that actually
     builds the DLL, package correctly, I'm just trying to get the XAML test to
     work.

  2. This causes weird bugs trying to import the TerminalAppLib project, for
     whatever reason. Unfortunately, it causes the TerminalApp types to not
     appear in the final manifest, so I think we'll need to reference that winmd
     manually.

  3. Make sure to include the `("UAP:Host", "Xaml")` bit in the test metadata.

  4. Now, the `RunOnUIThread` test actually passes. It won't work with our
     types, but _progress_

  I need to revert the App.xaml->TerminalApp change, because that's going to
  totally mess up the build. Full stop, that needs to happen.

  The problem we're running into now is that
  _ConsoleGenerateAdditionalWinmdManifests doesn't generate a .manifest for
  TerminalAppLib, so it never gets included into the Appxmanifest.

  I could try manually adding the TerminalApp types to the manifest prototype
  again. That's an option. But since I'll need to revert the App change anyways,
  idk if that'll matter. Maybe if we manually _don't_ include App.xbf in the
  output, and TerminalApp.App in the manifest?

This reverts commit 80e9e73.

This reverts commit 51bc3e7.

  Just don't include the App.xbf and it magic works?

  Somewhere after we create the TermControl we crash, but that's _so_ good man.
  We're so close.