Debugging support is broken after the most recent release

[baronfel]

Describe the bug

The most recent release updated to a version of FsAutoComplete that understood the concept of 'Reference Assemblies' - minimal assemblies that just expose the surface area of a DLL, with no implementations. This resulted in a change to the contents of the Output property of the Project type used to communicate project metadata between FSAC and Ionide. Previously, only the path to the actual implementation assembly was passed here, which meant that this field could be used by Ionide here to compute the path to the assembly to run. Now, this OutputFileOpt could be the ref assembly, which results in errors like the following:

A fatal error was encountered. The library 'hostpolicy.dll' required to execute the application was not found in '...\obj\Debug\net7.0\ref'.
Failed to run as a self-contained app.
  
The application was run as a self-contained app because '...\obj\Debug\net7.0\ref*.runtimeconfig.json' was not found.
If this should be a framework-dependent app, add the '...\obj\Debug\net7.0\ref*.runtimeconfig.json' file and specify the appropriate framework.

[baronfel]

Fixed in 7.18.1!