Drop windows desktop SDK depedency

[petarpetrovt]

Adding package reference to Core.System.ServiceProcess when targeting .NET 5.0 (without windows forms) gives the following error:

NETSDK1136 The target platform must be set to Windows (usually by including '-windows' in the TargetFramework property) when using Windows Forms or WPF, or referencing projects or packages that do so.

This PR drops the windows desktop SDK dependecy for netstandard2.0 target framework, Updates the obsoleted netcoreapp3.0 target framework with net5.0-windows and updates the package version to 2.0.

[cbenard]

Pulled it down to look at it. Looks great. Thanks for the great PR!

[cbenard]

Had to fix the broken publish to NuGet action. I wasn't sure if I'd have time to look into it, but looks like switching it to runs-on: windows-2019 fixed part of it and then the author has abandoned it, so I had to use someone else's forked fix.

Anyway, version 2.0.1 is now on NuGet. Thanks again!