Port fixes from 3.18 releases

[CharliePoole]

The following fixes to the 3.18.x releases need to be ported to version 4.

• Engine should honor the DOTNET_ROOT environment variable if set #1381
• ExtensionService does not validate the content of addins files #1415
• Spurious error is reported for non-test projects when running the solution #1465
• System.TypeLoadException : Could not load type 'System.Windows.IWeakEventListener' from assembly 'WindowsBase' #1466
• Console output is unclear about which console build is running #1467
• Unable to run nunit-console with VSProjectLoader that has a WPF 8.0 project #1468
• nunit console can't parse test case with special characters #1469
• Nunit console doesnt find selenium-manager.exe , works fine from visual studio #1488

[CharliePoole]

This issue has been resolved in version 4.0.0-beta.1

The release is available on:
GitHub.
NuGet packages are also available NuGet.org and
Chocolatey Packages may be found at Chocolatey.org