Support generate-method on nullable structs.

Simplify code for figuring out the name for a symbol in a feature.

Always keep foreach-variable when converting to for-loop

Use FailFast with diagnostics

Fix enum preselection in VB collection initializer

Change all the direct uses of `Environment.FailFast` to instead use
`FailFast.Fail`. The latter has diagnostics which are useful for determining why
unit tests are failing.

- Microsoft.DotNet.Arcade.Sdk - 5.0.0-beta.20171.1
Co-authored-by: Ndotnet-maestro[bot] <dotnet-maestro[bot]@users.noreply.github.com>

Port C# RemoveUnreachable code analyzer/fixer to shared layer

* Use globs in .projitems

* Revert EE changes

* Use DefaultLanguageSourceExtension

Port C# UseDefaultLiteral analyzer/fixer/tests to shared layer

* Update dependencies from https://github.com/dotnet/arcade build 20200318.1

- Microsoft.DotNet.Arcade.Sdk - 5.0.0-beta.20168.1

* Update dependencies from https://github.com/dotnet/arcade build 20200318.2

- Microsoft.DotNet.Arcade.Sdk - 5.0.0-beta.20168.2

* Update dependencies from https://github.com/dotnet/arcade build 20200320.1

- Microsoft.DotNet.Arcade.Sdk - 5.0.0-beta.20170.1

* Update dependencies from https://github.com/dotnet/arcade build 20200320.4

- Microsoft.DotNet.Arcade.Sdk - 5.0.0-beta.20170.4
Co-authored-by: Ndotnet-maestro[bot] <dotnet-maestro[bot]@users.noreply.github.com>

Revert "Merge pull request #42622 from gafter/records3-merge-2020-03-20"

This reverts commit 3c38a9a7, reversing
changes made to 20643918.

Simplify the progress system for find-references

Remove workspace dependency from 'use pattern matching'.

Merge release/dev16.6-preview2 to master

merge master into features/patterns3

Merge branch 'findUsagesProgress' of https://github.com/CyrusNajmabadi/roslyn into findUsagesProgress