Update to latest Xunit and Moq, fix test bugs, stop suppressing analyzers

[joelverhagen]

Currently we have a bunch of test bugs that are hidden by these problems:

• We are on old Xunit. Newer Xunit has improved source analyzers to show problems
  • Example problem: methods missing [Fact] or [Theory] meaning test cases weren't running at all
  • Example problem: unawaited Task or async void resulting assert does not get observed
  • Example problem: unused parameter in [Theory] meaning only one variant of the test was really running
• test.ps1 had broken file paths in several cases... meaning the UT projects weren't event running

Summary of changes:

• Move to xunit 2.9.0, xunit.runner.visualstudio 2.8.2 (latest) and clean up dependencies on Xunit
• Clean up minor build warnings
• Delete .editorconfig. All it does is suppress everything meaning these warnings/errors were hidden!
• Fix tests broken and unobserved due to test.ps1 path issue
• Improve test.ps1 to catch when tests don't produce result XML
• Use Assert.Single, Assert.Empty, Assert.Contains, etc per the Xunit analyzer
• Suppress xUnit1015 in two cases where we have a child class provide test data to a parent class [MemberData] (weird, but works)
• Suppress xUnit1032 in AccountsControllerFacts since we provide child classes for this generic class meaning the tests do actually run
• Improved the read only mode checks in EntitiesContext. It was possible to work around the check via SaveChanges variants
• Skip MvcBuildViews=true when building debug. This makes build.ps1 faster locally, does not affect CI/release.
• Move to Moq 4.20.70, set up HTTP response code due to changes in Moq

Progress on https://github.com/NuGet/Engineering/issues/5427.

[agr]

https://github.com/NuGet/Engineering/issues/5427 - related?

[joelverhagen]

NuGet/Engineering#5427 - related?

Yes, thank you! I will take ownership and do this too: