Merge master to release/dev16.6-preview1

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

Merge release/dev16.6-preview1 to master

See https://github.com/dotnet/runtime/issues/30539

Fix link, and "retail" should read "release"?

Do not simplify interpolation expressions on implicit receivers.

* Update dependencies from https://github.com/dotnet/arcade build 20200131.7

- Microsoft.DotNet.Arcade.Sdk - 5.0.0-beta.20081.7

* Update dependencies from https://github.com/dotnet/arcade build 20200201.2

- Microsoft.DotNet.Arcade.Sdk - 5.0.0-beta.20101.2

* Update dependencies from https://github.com/dotnet/arcade build 20200203.5

- Microsoft.DotNet.Arcade.Sdk - 5.0.0-beta.20103.5

Run naming styles on closed files

Provide context information for analyzer exceptions

* MethodSymbol and FieldSymbol equality fixes:
 - Defer the equality of method/field symbol to the substituted symbol when compared
 - Make the hashcode of substituted method/field defer to the original definition

Preserve "unsafe" when refactoring between properties and methods

Allow -launch to be used without -build

Annotate implementations of IEventSymbol

Annotate implementations of ILabelSymbol

Rename from IncludeNonNullableReferenceTypeModifier to IncludeNotNullableReferenceTypeModifier (#41332)

* Set TEMP environment variable to $TempDir on CI machines

https://github.com/dotnet/arcade/pull/4744 reverted setting the variable in `tools.ps1` due to issues it caused in other repos.

Merge master to release/dev16.6-preview1

Stop Simplifier.ReduceAsync removing empty arg lists from delegates

Fix for Visual Studio crashes when adding a parameter to a function

* Fix Pythia pooled objects wrappers

* Fix RPC

Fix issues in MetadataAsSource XML documentation comment conversion