Merge master to features/readonly-members

Merge master to features/readonly-members

Revise NullableWalker to use a two-state solution

Merge master to features/readonly-members

Reflects the changes described in https://github.com/dotnet/csharplang/pull/2214.

Range now looks optimistically for some special members with optional
parameters, but will fall back to the Range constructor if they aren't
present.

This change also removes all of the specialized codegen that was going
on with arrays and strings in favor of expected helpers or real members.

Merge remote-tracking branch 'dotnet/master' into pr/33648-revise-nullablewalker-to-use-a-two-state-solution

Undo arcade work arounds

* Fixes 33602

* respond to comments

I verified that this test crashes the compiler in Preview3
but no longer repros.

Fixes #33537

Marshal.SizeOf is not a direct replacement for `sizeof` and the issues around it are subtle.

Fix #26513

Now that we have the version of arcade that supports
Microsoft.Net.Compilers.Toolset we can remove a few work arounds.

Mark Roslyn.VisualStudio.DiagnosticsWindow as a build dependency…

[master] Update dependencies from dotnet/arcade

* Nullability for NVT with no constructor argument:
- Explicitly check if an object creation is a nullable value type
- Set its state to nullable when it is the default constructor that is being called
- Update tests

Mark Roslyn.VisualStudio.DiagnosticsWindow as a build dependency of Microsoft.VisualStudio.IntegrationTest.Setup

Fixes #33762

Non-private readonly fields are PascalCase

Auto-attach debugger to target instance of Visual Studio during integration tests

Enable C# 8.0 in the code base

Merge master to features/readonly-members

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19127.8

Merge dev16.0 to master

* Update dependencies from https://github.com/dotnet/arcade build 20190116.1

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19066.1

* Update dependencies from https://github.com/dotnet/arcade build 20190117.6

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19067.6

* Update dependencies from https://github.com/dotnet/arcade build 20190118.4

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19068.4

* Update dependencies from https://github.com/dotnet/arcade build 20190119.2

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19069.2

* Update dependencies from https://github.com/dotnet/arcade build 20190120.2

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19070.2

* Update dependencies from https://github.com/dotnet/arcade build 20190122.5

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19072.5

* Update dependencies from https://github.com/dotnet/arcade build 20190123.5

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19073.5

* Update dependencies from https://github.com/dotnet/arcade build 20190130.6

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19080.6

* Update dependencies from https://github.com/dotnet/arcade build 20190131.3

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19081.3

* Update dependencies from https://github.com/dotnet/arcade build 20190201.16

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19101.16

* Update dependencies from https://github.com/dotnet/arcade build 20190202.1

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19102.1

* Update dependencies from https://github.com/dotnet/arcade build 20190203.1

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19103.1

* Update dependencies from https://github.com/dotnet/arcade build 20190204.18

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19104.18

* Update dependencies from https://github.com/dotnet/arcade build 20190205.5

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19105.5

* Update dependencies from https://github.com/dotnet/arcade build 20190206.4

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19106.4

* Update dependencies from https://github.com/dotnet/arcade build 20190207.1

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19107.1

* Update dependencies from https://github.com/dotnet/arcade build 20190208.1

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19108.1

* Update dependencies from https://github.com/dotnet/arcade build 20190212.3

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19112.3

* Update dependencies from https://github.com/dotnet/arcade build 20190213.1

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19113.1

* Update dependencies from https://github.com/dotnet/arcade build 20190214.4

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19114.4

* Update dependencies from https://github.com/dotnet/arcade build 20190215.1

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19115.1

* Update dependencies from https://github.com/dotnet/arcade build 20190219.2

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19119.2

* Update dependencies from https://github.com/dotnet/arcade build 20190221.1

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19121.1

* Update dependencies from https://github.com/dotnet/arcade build 20190221.5

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19121.5

* Update dependencies from https://github.com/dotnet/arcade build 20190222.3

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19122.3

* Update dependencies from https://github.com/dotnet/arcade build 20190223.1

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19123.1

* Update dependencies from https://github.com/dotnet/arcade build 20190224.1

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19124.1

* Update dependencies from https://github.com/dotnet/arcade build 20190225.2

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19125.2

* Update dependencies from https://github.com/dotnet/arcade build 20190226.6

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19126.6

import the base type to work around breaking change

* Exposes additional compilation options to the scripting API

Closes #32667

* Accordingly to the PR review

Remove empty lines.
Add OptimizationLevel to the VisualBasicCompilationOptions.
Add tests that ensures ScriptOptions are applied to the compilation.

Regex completion (no completion-suffix work)

Merge master to features/readonly-members

This change enables C# 8.0 use in the code base as well as moving the
recommended Visual Studio version to 2019 Preview 4.  The following
features are now allowed to be used:

- `switch` expressions
- recursive pattern matching
- `using` declarations
- `static` local functions
- local / parameter shadowing in local functions / lambdas
- `null` coalescing assignment
- `async` streams: keep this out of our public API surface for now as we
don't want to block unification with netcoreapp in the future.

Before getting into the features which are off limits I wanted to
outline how compiler toolsets work in this repository. There are three
toolsets we need to consider when adopting new features:

1. The compiler toolset which provides the IDE experience: Intellisense,
syntax highlighting, etc ...
1. The compiler toolset which is used when the solution is built. This
is explicitly different than the compiler toolset which ships with the
MSBuild driving the compilation.
1. The compiler toolset is built from source on every PR and used as the
toolset for the PR (overriding 2 above).

That being said the following features are offlimit for now:

- Index / Range: the API surface area, including the parts the compiler
depends on, underwent significant churn for .NET Core Preview 3. Until
we converge it means toolsets 1 and 2 can be a bit out of sync.
- `unmanaged` generic `struct`: this is not included in VS2019 Preview 4
and hence using it would make the IDE experience poor.
- Nullable Reference Types: this area is under active churn and we could
easily get into a situation where toolsets 2 and 3 disagreed on code
checked into the repository creating unmergeable PRs. As such we're
holding off on this in master for now. Until then please use the branch
[features/NullableDogfood](https://github.com/dotnet/roslyn/tree/features/NullableDogfood)
to dogfood NRT. This will be merged back into master closer to
Dev16.0GA.

Note: This change only affects the C# compiler toolset. There are no
changes to our MSBuild or .NET Core SDK toolsets. Those will be coming
soonish though.