This isn't used yet in this commit, but will allow us to audit which
tests are claiming they need WPF/STA threads but don't.

Right now Debug.Assert throws up a UI dialog when the assert fails,
even in tests. Fixing this is being tracked by #2796, but until then
we can switch over this single problem site.

This code was used as the basis for WpfFact, and we exclusively use
the latter.

Set mac PR tests to run on trigger phrase only temporarily.

Remove caching of declaring syntax references for symbols in analyzer… 

Watson: Fix crash when accessing CodeProperty.OverrideKind property for property not contained by a type

add ResultDir to TestResult rather than retrieving it from ResultsFil…

Upgrade NuGet to 3.4.0.247 and increase restore timeout

NuGet's timeout for restoring us is too short, causing a
timeout on our internal build machines when the CPU is
under high load. We need to upgrade to 3.4 to control
this.

Increase this to 20 minutes from the default 5 minutes.

Delete build/ToolsetPackages/project.lock.json

Code Model shouldn't expose code elements for invalid members (e.g. methods in namespaces) or fire events for them

This change ensures that Code Model never considers members that are un-supported, such as methods declared directly inside of namespaces. It's possible that we may eventually add support in code model for top-level methods specifically within script code, but we don't support today.

Add support for NotInheritable and NotOverridable

Merge update 1 branch to master

Disable FullQualifiedTests.TestCaseSensitivity3 due to flakiness

Whereas other project.lock.json files are checked in because other
tools consume them, this is consumed by nothing. All it does is make
merging between branches more annoying.

Watson: Fix crash when accessing CodeProperty.OverrideKind property for property not contained by a type

The root cause is based on analysis of a Watson crash dump with ~300 hits. The call stack looks like this:

```
microsoft_visualstudio_languageservices_csharp_ni!Microsoft.VisualStudio.LanguageServices.CSharp.CodeModel.CSharpCodeModelService.GetOverrideKind
microsoft_visualstudio_languageservices_implementation_ni!Microsoft.VisualStudio.LanguageServices.Implementation.CodeModel.InternalElements.AbstractCodeMember.get_OverrideKind
envdte80!EnvDTE80.CodeProperty2.get_OverrideKind
microsoft_visualstudio_modeling_artifactmapper_vshost!Microsoft.VisualStudio.Modeling.ArtifactMapper.VSHost.CodeController+AllLanguages+AttributeIsNew.GetAttribute
microsoft_visualstudio_modeling_artifactmapper_vshost!Microsoft.VisualStudio.Modeling.ArtifactMapper.VSHost.CodeController.GetAttribute
microsoft_visualstudio_modeling_artifactmapper_vshost!Microsoft.VisualStudio.Modeling.ArtifactMapper.VSHost.CodeController.GetProperties
microsoft_visualstudio_modeling_artifactmapper_vshost!Microsoft.VisualStudio.Modeling.ArtifactMapper.VSHost.CodeHandler+CodeModelCache.FireAddEvent
microsoft_visualstudio_modeling_artifactmapper_vshost!Microsoft.VisualStudio.Modeling.ArtifactMapper.VSHost.CodeHandler+CodeModelCache.AddElement
microsoft_visualstudio_modeling_artifactmapper_vshost!Microsoft.VisualStudio.Modeling.ArtifactMapper.VSHost.CodeHandler.WalkCodeElement
microsoft_visualstudio_modeling_artifactmapper_vshost!Microsoft.VisualStudio.Modeling.ArtifactMapper.VSHost.CodeHandler+CodeModelCache.AddElementWithChildren
microsoft_visualstudio_modeling_artifactmapper_vshost!Microsoft.VisualStudio.Modeling.ArtifactMapper.VSHost.CodeHandler+CodeModelCache.RebindChildren
microsoft_visualstudio_modeling_artifactmapper_vshost!Microsoft.VisualStudio.Modeling.ArtifactMapper.VSHost.CodeHandler+CodeModelCache.ChangeElementUnknown
microsoft_visualstudio_modeling_artifactmapper_vshost!Microsoft.VisualStudio.Modeling.ArtifactMapper.VSHost.CodeHandler+CodeModelCache.ChangeElement
microsoft_visualstudio_modeling_artifactmapper_vshost!Microsoft.VisualStudio.Modeling.ArtifactMapper.VSHost.CodeHandler.codeModelEvents_Changed
```

After analysis of the dump, I was able to reproduce the call stack using the following steps:

1. Create new Class Library
2. In the Solution Explorer, right-click on Class1.cs and choose View->View Class Diagram from the context menu.
3. Add a new property inside Class1.
4. Copy and paste that property *twice* inside the enclosing namespace of Class1.

This causes an "Unknown" code model event to fire which the Class Designer responds to by digging through its elements and accessing various properties. One of those properties (`OverrideKind`) retrieves the containing type of the element, but that's null for the properties contained in a namespace and the call throws. So, the fix is to add a couple of simple null checks. Note that this affects all members, so I added tests for fields, events and methods as well.

Gracefully handle analyzer diagnostics with location outside the current compilation

ResultsFilePath can be null in cases where xunit failed to save one. so rather than using ResultsFilePath
to figure out ResultDir, we will save the dir in the TestResult along with the filepath.

Fix VB outlining banner text to not break onto multiple lines

Fix C# cast simplification issue where removal of a cast can break an implicitly-typed array

Revert "Merge pull request #6903 from mavasani/MakeAnalyzerExecutorAsync"

This reverts commit 268e7d38, reversing
changes made to 98790c02.

Conflicts:
    src/Compilers/Core/Portable/DiagnosticAnalyzer/AnalyzerDriver.cs