* Use explicit namespace for proprietary resources

The Roslyn code base originated with all of our resource reference /
impl DLLs being checked into a single utility project. At the point we
moved to Git and went OSS these single utility project was factored into
two projects for a number of reasons.

1. Keeping DLLs we didn't have license for private
1. Letting us put large binaries into a NuPkg file vs. polluting Git
   history

When this split occured the namespaces for the utility projects were not
updated. That means many types in our public and private resource
projects have the same name. This makes it **really** difficult to
determine where types and resources are coming from.

This change adds an explicit namespace to the proprietary resource
assembly. This will help make it clear which resources come from it.

* Fix version

* Remove version ambigutiy

* Fix test failure

Rename types to not collide with the much more relevant Workspace equivalents

* Move to the .NET 5 SDK

This is necessary for us to test features like covariant returns because
we need to be able to target `net5.0` in our unit test projects.

Issues encountered in this update:

- WinRT is no longer supported in .NET 5. As a result we no longer multi-target
.NET Core in our WinRT test assembly as well as having to disabling a
few WinRT tests in others.  https://github.com/dotnet/runtime/issues/37672
- Change our Debugger Proxy tests to react to a runtime change
https://github.com/dotnet/runtime/commit/c362923cae8543b5092b2115f169411ee7dd4763
- Work around .NET5 P6 bug https://github.com/dotnet/sdk/issues/11862

Remove wait for out of process start from OnLoadedAsync as it has not…

Enable BasicLineCommit.CommitOnSave

Enable CSharpInteractiveCommands.VerifyPreviousAndNextHistory

Switch 'use auto prop' to use NRT and make us more null safe.

Fixes #46148

Remove wait for out of process start from OnLoadedAsync as it has not cancellation token.  The wait will instead occur in ActivateAsync with cancellation

Enable GenerateMethodInClosedFile

Invoke IInteractiveWindow members from the UI thread

Add the name of the current type to the exception we throw in an unsupported case.

Add test for switch expression delegates

Merge release/dev16.8-preview1 to master

Enable CompletionUsesTrackingPointsInTheFaceOfAutomaticBraceCompletion

Add Arcade package feed to PublishData

Rename ComilerTraitDiscoverer.cs to CompilerTraitDiscoverer.cs

Closes #34637

See #40160

Closes #18779

Closes #33825

They are recorded in #46171

Enable .NET Core integration tests

Add support for navigation to mapped file paths.

[Dogfooding] Enforce existing IDE layer code style rules in VisualStudio layer

Closes #39588