Version update

[wforney]

• Updated all projects to VS 2019, .NET Framework 4.8, and latest Windows 10 target for the C++ project

[nvella]

Hi @wforney, seems mostly solid. There are a few errors in the CI build as it's still running 2017, appveyor.yml and build.ps1 may need to be updated. https://ci.appveyor.com/project/dotnetfoundation/openlivewriter/builds/27712275#L246

[nvella]

Hi @wforney, I found some docs which might help out;
https://github.com/microsoft/vssetup.powershell/blob/develop/docs/VSSetup/Select-VSSetupInstance.md#-version

It might be worth changing the version specifier from [15.0,16.0) to [16.0,17.0) - this specifies exactly v16 (Visual Studio 2019). Cheers 👍