Add IgnorePortablePDBsInStackTraces in .config files

[jcansdale]

• IgnorePortablePDBsInStackTraces
  [Umbrella] Add IgnorePortablePDBsInStackTraces in config files for partner tools dotnet/roslyn#25088

• AppContext
  https://docs.microsoft.com/en-us/dotnet/api/system.appcontext?view=netframework-4.7.2

https://twitter.com/jcouv/status/1007113347668381696

TODO

• Don't set TargetFrameworkName: .NETStandard,Version=v2.0 when targeting a .NET Standard project
  This is messing up quirks mode, see Run using .NET Framework (and "quirks mode") that project.json is targeting #29

https://github.com/jcansdale/TestDriven.Net/blob/73eba3e5d867f76deb49fa6c1de115f89330f17d/TestDriven.NET/TestDriven.TestRunner/AppDomainTestRunner.cs#L63

See "quirks" mode defaults:

• Reference source
  https://github.com/Microsoft/referencesource/blob/master/System/sys/AppContextDefaultValues.Defaults.cs