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

Our best guess is we ran naming styles on open files only for two
reasons:

1. At the time, we only supported .editorconfig in-proc, so
   out of proc wouldn't have used the right settings.
2. Even if we were running in-proc, there might have been performance
   issues since we were running across a lot of files.

Neither of these concerns apply at this point: we now support
.editorconfig out of proc (both in the legacy path and the new path) and
since we're already running other analyzers that use .editorconfig,
the cost of processing it will exist regardless.

Make ValueText return empty instead of null

Target netcoreapp3.1

Merge master to release/dev16.6-preview1

Name suggestions don't contain suggestions starting with a digit.