Add editor support for inferred import completion

[jessetrinity]

Automatic import completion settings are currently available in the latest releases of Visual Studio and VSCode via 22236 Support services settings.

The behavior of getQuotePreference allows the quote style to be inferred from pre-existing imports. There is not currently a supported to way to get back into this state once the quote style has been explicitly set to single or double.

An "auto" option should be added to UserPreferences to support this behavior.