Use pattern matching in a few more places.

Fix significant wrong translation in CodeStyle.Resources.zh-Hans.xlf

Will be consumed by tooling to recommend LangVersion 

* Add all nullable-related warnings to ErrorFacts

* Fix test failures and add a bit more coverage

* Emit tests

* Report rude edits for unsupported DIM operations

* Allow EnC tests to specify TFMs to build against

* EnC: test against netcoreapp30

* Test fixes

* Fix merge

Expand introduced using statement to include encompassed locals

Fixes #36241

Fixes #37187

Enable .editorconfig discovery by default

Implements https://github.com/dotnet/csharplang/issues/2389
Fixes #35958

Note that the switch expression conversion is not a standard implicit conversion.  Specifically, it should not be considered as a valid implicit conversion as input to a user-defined conversion, as that could permit two chained user-defined conversions.

Also changes binding of switch expression to ECMA so it can interact properly with switch expressions.
Fixes #14965

 Avoid boxing in string concatenation 

- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19364.1

Resolves #33344

Relates to #29821
Fixes #34409

Merge liveshare changes to do dual insertion.

* Update dependencies from https://github.com/dotnet/arcade build 20190711.7

- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19361.7

* Update dependencies from https://github.com/dotnet/arcade build 20190712.5

- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19362.5

* Update dependencies from https://github.com/dotnet/arcade build 20190713.1

- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19363.1

Show infobar for recommending installation of FxCopAnalyzers NuGet/VSIX

Address PR feedback and add an internal abstract property `SyntaxEditorBasedCodeFixProvider.CodeFixCategory` to determine the category of code fixes offered by our code fixers.

Completion timebox

Fixes #29819

Move refactorings to common helpers

Move 'Wrapping' code actions down to 'Feature' layer.

* Top-level types enumeration refactoring

* Simplify DefinitionMap

* Include namespaces in synthesized definition map

* Add SynthesizedNamespaceSymbol

* Embedded Attributes

* Test synthesized attributes

* Clean up EnC tests

* Clean up symbol matcher tests

* Ref readonly return type, in parameter symbol matching tests

* Enable using ref readonly returns, in parameters, ref structs during debugging

* More tests

* ReadOnly struct members

* Fix langauge version mismatch

* Merge fix ups

* Feedback, skip tests