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

Rename TypeArgumentsNullableAnnotations to TypeArgumentNullableAnnotations

* dotnet/master:
  Fix master build (#37163)
  Add error for multiple null suppressions (#37139)
  Check for uninitialized non-nullable field-like events (#37073)
  EnC emit tests for C# 8.0 patterns (#37025)
  Update dependencies from https://github.com/dotnet/arcade build 20190710.8
  Update dependencies from https://github.com/dotnet/arcade build 20190709.6
  [master] Update dependencies from dotnet/arcade (#37001)
  Add annotations to HostWorkspaceServices.cs and HostLanguageServices.cs
  Add nullable annotations to members in Solution.cs, SolutionInfo.cs, and SolutionState.cs
  Annotate Contract.cs
  Add nullable annotations and fixes to Workspace.cs
  Fix typo in documentation comment for Workspace.Dispose
  Check in copy of NullableAttributes.cs copied from coreclr
  Use switch expressions to simplify GetAccessibilityAndModifiers

[master] Update dependencies from dotnet/arcade

Use switch expressions to simplify GetAccessibilityAndModifiers

Fixes #37111

Fixes #30067

* EnC LocalSlotMappingTests for C# 8.0 patterns
* PDBTest
* EditAndContinueTest

- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19360.8

Add nullable annotations to parts of the Workspace API

- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19359.6

* Update dependencies from https://github.com/dotnet/arcade build 20190704.2

- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19354.2

* Update dependencies from https://github.com/dotnet/arcade build 20190705.2

- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19355.2

* Update dependencies from https://github.com/dotnet/arcade build 20190706.1

- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19356.1

* Update dependencies from https://github.com/dotnet/arcade build 20190708.1

- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19358.1

* Update dependencies from https://github.com/dotnet/arcade build 20190709.1

- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19359.1

Fixes #36963

The semantic model often creates ReducedExtensionMethods for the public API,
but the creation of ReducedExtensionMethod does constraint checking, which
requires a compilation, which isn't always available. This change removes constraint
checking from all creation of ReducedExtensionMethod and adds asserts that we
always have a compilation during constraint checking.

Fixes #37021

Don't show full attribute type name if in attribute name context