The latest version of ilasm produced by coreclr is now a fully
independent executable; it no longer depends on having a full runtime
laid down next to it.

This means we can vastly simplify how it is deployde in our
infrastructure. The package can now be included and have ilasm manually
copied out. This is similar to the approach that we take for our
diasymreader native dependencies.

closes #37582
related #25930, #25144

* Remove RoslynProjectType

* Remove ToolsVersion, namespace from Project tags

* Remove updating of MSBuildAllProjects

* Update BuildBoss

* Delete DeployTooolsetCompiler

* Use Arcade testing targets

* Skip CodeStyle tests on Mono

* Include net472 in test target frameworks for Mono

* Remove incorrect file existence check.

* Update ADO integration test yaml

After working with the CoreClr team it turns out part of our CoreClr
flakiness on Linux is due to bugs fixed in netcoreapp2.1. Given that and
that our consumers are all on netcoreapp2.1 already I'm moving us to
2.1.

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

* Remove dependency on Microsoft.NET.Test.Sdk

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.

The CLI toolchain only supports string literals inside of a RESX file.
Other blobs, such as a reference to a file on disk, are not supported.
Instead their value gets embedded directly as a string literal (type is
ignored). Only supported mechanism is to embed them as a manifest
resource stream.

https://github.com/Microsoft/msbuild/issues/2221

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.

The portable test utilities project already multi-targets between
netstandard, netcoreapp and desktop. Having part of the desktop code
exist in a separate assembly makes it even harder to multitarget our
test projects. Combining them all together and fully embracing
multitargeting here.

This is in preparation of moving several other compiler test projects to
test against coreclr / mono.

Many of our VB projects today rely on having an empty default namespace
and explicitly specifying the full namespace in source. In the new SDK /
dir props world this can only be done by explicitly marking the
namespace as empty in the project file. Can't do the centralized control
that we do today.

This primarily moves us to the 2.2.0 version of xunit. In order to make
that transition though a number of other changes needed to happen as
well:

1. Needed to move our desktop target to 4.6.1. This should've been
required some time ago but we were essentially depending on bugs in the
SDK / NuGet.
1. Remove the DeployCoreClrTestRuntime project. This entire idea
depended on having the xunit.console.netcore package. This has since
been deleted and doesn't work with the 2.0 SDK.
1. Remove the deploy compiler tools project. Can just use dotnet exec
now and that's much more efficient.
1. Resolve a new ambiguity with KeyValuePair. A helper of ours now
exists in netcoreapp2.0.

I fully expect a number of Jenkins legs to fail with this change: build
correctness, coreclr and ubuntu. But I want to validate our other legs
and am still trackind down answers needed to fix the others.

1. Add IsChecked flag for IIncrementExpression and ICompoundAssignmentExpression
2. Add back VB specific binary operator kinds
3. Add more unit tests and fix baselines of existing tests

In the new SDK we no longer have a need for ProjectGuid. This change
will:

- Remove ProjectGuid from project files
- Remove Name + Project items from ProjectReference entries
- Change BuildBoss to enforce both of these items

Some test projects have checked in cs\vb files as test assets. Group them with None\Content and add comments to the effect that they are valid removes.

added vb unary operator tests

Migrated the remainder of our code base to use the new SDK via the
ConvertPackageRef tool.

https://github.com/jaredpar/ConvertPackageRef

Fixes #10856

```
    public interface ITupleExpression : IOperation
    {
        /// <summary>
        /// Elements for tuple expression.
        /// </summary>
        ImmutableArray<IOperation> Elements { get; }
    }
```

Fixes #18300