enabled the nullable feature, either on the command line
or via a nullable enable directive.

Wire NullableWalker snapshotting to the public SpeculativeSemanticModel apis

Add some nullability tests for Generate Type and fix one bug

Closes https://github.com/dotnet/roslyn/issues/30316

Also add extension methods to help with nullability

* dotnet/master: (85 commits)
  Don't complete statement when typing semicolon inside comments in an argument list (#36521)
  Set focus to editor before finding text
  Add a bunch of nullability support to some code generation helpers
  Add 'annotations' and 'warnings' support to nullable directive (#36464)
  Fixed IDE services touching `notnull` constraint (#36508)
  Update compiler toolset to arcade version (#36549)
  Fix for 923157
  Do not include value types in NullableAttribute byte[] (#36519)
  Fix a deadlock in InvokeOnUIThread
  Apply a hang mitigating timeout to UI thread operations
  Move to a different lowering from for nullable value types to work around a bug in TransformCompoundAssignmentLHS. Addressed PR feedback.
  Fix stack overflow in requesting syntax directives (#36347)
  crash on ClassifyUpdate for EventFields (#35962)
  fixing bad merge with refactoring that was checked in later
  added basic completion statement telemetry
  Remove duplication in AbstractSymbolCompletionProvider.CreateItems
  Disable move type when the options service isn't present (#36334)
  Fix crash where type inference doing method inference needs to drop nullability
  Revert "Use IVsSolution to look up IVsHierarchy by project GUID (#35746)"
  Fix parsing bug in invalid using statements (#36428)
  ...

Set focus to editor before finding text

Add a bunch of nullability support to some code generation helpers

* Fix for typing semicolon inside comments in an argument list

* Change to previously existing method

* Fix

Closes #36401

Merge release/dev16.2-preview3 to master

* Add optional [warnings | annotations] keyword to nullable directive

* pragma warning <setting> nullable -> nullable <setting> warnings

* Implement /nowarn:nullable

Fix stack overflow error in Complete Statement 

Fixes #36037

Plumb speculative model through to analyzers. Expand the tests of the speculative model to show both inputs to the nullable walker and inferences from the nullable walker in the speculated code.

Apply a hang mitigating timeout to UI thread operations

Implement subset-based ordering for naming rules

Update naming styles to ensure .editorconfig is the code style "source of truth"

Change `??=` for nullable value types as specified in LDM

added basic completion statement telemetry

Remove duplication in AbstractSymbolCompletionProvider.CreateItems

* dotnet/master: (63 commits)
  Fix stack overflow in requesting syntax directives (#36347)
  crash on ClassifyUpdate for EventFields (#35962)
  Disable move type when the options service isn't present (#36334)
  Fix crash where type inference doing method inference needs to drop nullability
  Fix parsing bug in invalid using statements (#36428)
  Do not suggest or diagnose use compound assignment when right hand of binary operator is a throw expression
  Add option to emit nullable metadata for public members only (#36398)
  Added null checks on F# external access services (#36469)
  Deal with discovering extra .editorconfig files
  Re-enable MSBuildWorkspaceTests.TestEditorConfigDiscovery
  Add support to VisualStudioMSBuildInstalled to support minimum versions
  Fix configuration of accessibilities in editorconfig
  Shorten a resource ID
  Revert "Extract the RDT implementation for Misc files and VS open file tracker"
  Add nullability support to use local function
  Add EditorFeatures.WPF dependency to F# ExternalAccess
  Ensure NullableWalker.AsMemberOfType locates the right new container for the member. (#36406)
  Replace `dynamic` with `object` when substituting constraints. (#36379)
  Add some string descriptions
  Adjust type of out var based on parameter state (#36284)
  ...

Revert 35746

Move to a different lowering from for nullable value types to work around a bug in TransformCompoundAssignmentLHS. Addressed PR feedback.

Fixes #36346

Fix crash where type inference doing method inference needs to drop nullability

Fix #36060: Group Completion Providers using IsExclusive