* Use Microsoft.NET.Sdk.WindowsDesktop for XAML projects

* Adds nullability, removes dead code.

* Clean up RemoteHostClient exception and lifetime handling

* Nullables

* JsonRpcEx disposal cleanup

* Nullables

* Refactor abstract JsonRpcEx to sealed RemoteEndPoint

* Use RemoteEndPoint for ServiceHub services

* Move ctor

* Use RemoteEndPoint in ServiceHubRemoteHostClient

* Minor cleanup of log messages

* JsonRpcTargetOptions

* Use RemoteEndPoint in CodeLens, tests

* Inline Extensions.InvokeAsync methods into RemoteEndPoint

* Remove unnecessary invoke methods

* Unify exception handling

* Allow null arguments in remote invocation

* Simplify ClientDirectStream

* Fold ClientDirectStream and ServerDirectStream into RemoteEntryPoint

* Feedback

* Fix test

This removes the hard dependency on the editor packages so we can
still support loading in 16.3. The unit tests must be disabled that
depend on the new support, but everything else will continue to
function.

packages

Closes #35071

See #35071

Fixes failure to correctly restore packages within Visual Studio 2019 RC.

* Revert "Revert "Interactive projects refactoring (#29069)""

This reverts commit e0a8124f.

* Fix bad merge

This reverts commit 41fb51d2.

Remove Repl projects

Remove Microsoft.VisualStudio.InteractiveServices project

Remove Microsoft.CodeAnalysis.InteractiveEditorFeatures

Rename InteractiveEditorFeatures to EditorFeatures.Wpf

Remove empty resource files

Reduce InteractiveFeatures dependencies

Merge InteractiveComponents content into Roslyn.VisualStudio.Setup VSIX

Rename InteractiveFeatures to InteractiveHost

Hook fatal error handlers

Workaround warning CS1574

Exclude CreateTemplateManifestsCacheFile

Do not include satellite assemblies in DesktopHost directory

Remove VB interactive menu item

Delete VisualBasic.EditorFeatures.Wpf

Delete more unused VB interactive code

Related issue: https://github.com/dotnet/roslyn/issues/25145
This PR add the function to VS and let use to pull members up via quick action

* Move xunit package references to Roslyn.Toolsets.Xunit.targets

* Remove dependency on Microsoft.NET.Test.Sdk

* NuGet packaging

* Add missing VS package references

* Fix scripts

* Add comment on Workspace.Desktop references with PrivateAssets

* Fix Microsoft.NETCore.Compilers package

* Fix up references

* Build fixes

* Correct OutputPath for package projects

* Use NuGetRepack to force exact versions in per-build packages

Newer editor packages are now properly authored that means we don't have
to explicitly yank out the contents of the package.

The C# syntax tests were missing a reference to xunit.runner.visualstudio
which prevented them from working in the Test Explorer in 15.8 Preview.
Rather than just adding a reference to this one test, I've added a reference
to the root test utilities project, that almsot every test references, and
deleted the explicit references in the test leaf projects. This should
hopefully be a more robust method of using the XUnit VS test adapter.

Even though Roslyn can only every be deployed where at least net461 or netcoreapp2.0 is available Roslyn cannot depend on netstandard2.0 assemblies. This is due to the setup of Visual Studio which has a minimum target of net46 and hence only deploys netstandard1.3 facades. In order to prevent netstandard2.0 versions of NuGet references to deploy, at build or test, we must limit the desktop target framework used in our projects to net46.

There is nothing functionally wrong with having our tests target net461. At the same time though it would mean our tests were running against the netstandard2.0 version of references, such as System.Collections.Immutable, which is not what we deploy against. Hence not testing what we ship which creates a small but real hole.