Automate activatable classes instead of manually creating manifest file

Summary

Having to declare activatable classes in the consuming app is a pain! There should be a way around it. When I create a new WinUI 3 C++ app and try to use a C# CsWinRT NuGet package, I have to declare all of the activatable classes before using them.

  <file name="WinRT.Host.dll">
    <activatableClass
        name="ClassLibrary1.Class1"
        threadingModel="both"
        xmlns="urn:schemas-microsoft-com:winrt.v1" />
    ...
  </file>

Otherwise, I get the Class not registered exceptions.

Exception thrown at 0x75E6E7A2 (KernelBase.dll) in App28.exe: WinRT originate error - 0x80040154 : 'Class not registered'.
Exception thrown at 0x75E6E7A2 in App28.exe: Microsoft C++ exception: winrt::hresult_class_not_registered at memory location 0x010FC38C.
Exception thrown at 0x75E6E7A2 in App28.exe: Microsoft C++ exception: [rethrow] at memory location 0x00000000.

There at least should be a way for a NuGet package author to include these class registrations so that consuming apps don't have to!