Delete Roslyn's ICommandHandler interface and all support code

Implement formatting suppression

Fix smart indent with hard tabs (merge to master)

Reduce allocations in DiagnosticIncrementalAnalyzer

typo: ahve -> have

Improved formatting of comments and suppressions

* Optimize GetSolutionUpdateStatusAsync for stepping in absence of changes

Fixes #16681
Fixes #38224

- Microsoft.DotNet.Arcade.Sdk - 5.0.0-beta.19476.6

Fixes #38819

* Update dependencies from https://github.com/dotnet/arcade build 20190918.2

- Microsoft.DotNet.Arcade.Sdk - 5.0.0-beta.19468.2

* Update dependencies from https://github.com/dotnet/arcade build 20190919.4

- Microsoft.DotNet.Arcade.Sdk - 5.0.0-beta.19469.4

* Update dependencies from https://github.com/dotnet/arcade build 20190919.8

- Microsoft.DotNet.Arcade.Sdk - 5.0.0-beta.19469.8

* Update dependencies from https://github.com/dotnet/arcade build 20190920.9

- Microsoft.DotNet.Arcade.Sdk - 5.0.0-beta.19470.9

* Update dependencies from https://github.com/dotnet/arcade build 20190923.5

- Microsoft.DotNet.Arcade.Sdk - 5.0.0-beta.19473.5

* Upgrade msbuild-xcopy version to 16.3

* Also specify 16.3 as the required VS version

* Update contributor docs to link .NET Core 3 as the build SDK

* Update packages to fix NuGet warnings

A new NuGet warning was introduced that requires a workaround

see https://github.com/NuGet/Home/issues/8583

* Embed VB runtime by default

Add support to use editorconfig for set severity command in the Analy…

* completion leaking cancellation exception

* code review feedback

* feedback addressed

* fixing more merge conflicts

* Update CommitManager.cs

Pass the actual code action span to the server when calculating code …

Now that the old code is dead, we don't need to qualify things anymore.

My previous commit deleted this interface and a constructor that
consumes it. But TypeScript is still MEF importing the interface just
to pass it to the constructor; this adds both of those back. Once
TypeScript is off of this constructor this commit can be reverted
verbatim.

Now that the editor has their own public version of this API, and all
code has been migrated to use the new system, we can delete all of the
code that was supporting the old handlers. It may be surprising that
much of this code was dead, but the command handler list that was being
invoked by all of this was indeed empty.

The intent of this particular commit is to be a fairly mechanical change
that leaves other bugs or strangeness in place. In particular,
DebuggerIntelliSenseFilter had a special ExecuteVisualStudio2000 that
removes the buffer's read-only flag, but in many codepaths we never
set that back. In other cases, we also ignored the HRESULT that came
from the next filter in the chain. These all appear to be bugs, but I
won't touch them for now.

There's also some remaining work happening in
AbstractOleCommandTarget.Execute.cs that probably should either be moved
to the core editor code (if it wasn't already), or into the command
handlers of Roslyn itself.

The command was ultimately being made available not because our command
handler said it should be, but our implementation of QueryStatus
in AbtractOleCommandTarget was unilterally saying the command is
available. This moves that into here.