Break types into their own files.

Extract a service component from Add-using independent of the CodeFixProvider

Add json converters for core Add-Using type.

Add add-using option to run out of process, and update tests to run both codepaths. (Note: add-using OOP not actually implemented yet).

Fix Extract Method operations within an event accessor

Fix IDE0009 false positive on expressions qualified with 'base.'

	Remove direct access to the IPackageInstaller service from add-usings search engine