Enable nullability by default in Roslyn

Update TypeImportCompletionProviderTests with records

Delete unused method

Merge release/dev16.8 to master

Implement redundant equality analyzer

Remove readonly on auto-property when a setter is needed

Add records support in navigate to

Fix typo in public API doc

Switch internal type to use immutable arrays.

[master] Update dependencies from dotnet/roslyn

Disable hash collision resistance for user data

Provide required callback targets

Fix xml attribute name classification

MessagePack is not able to deserialize SuccessfulConflictResolution with
a collision resistant equality comparer due to the use of DocumentId as
a dictionary key.

Fix failure to dispose RemoteWorkspace in tests

Fix cancellation handling in Parallel.For