* Remove unintentionally added extra option.
* Rename NavInfo property to NavInfoFactory.
* Add fallback to metadata-as-source if NavInfo can't be retrieved for some reason.
* Use [ExportLanguageService] attributes rather than language service factories.
* Add NavInfo tests for generic methods and types
* Add negative NavInfo tests for parameters, locals and labels
* Rename UsePreviewTab option to PreferProvisionalTab to remove some confusion around what it does, and document it.