Fix enum class switch_check detection

Fix enum class switch_check detection

Summary:
Enum class and Enum class labels have the same `Tnewtype` "pattern" and the
existing code doesn't detect enum classes correctly. This diff makes sure we
don't mix enum class members with enum class labels.

This diff also does minor improvements (correctly displaying `enum` vs `enum class` when relevant)

Reviewed By: madgen

Differential Revision: D33395957

fbshipit-source-id: c1b9fc78a87a4fcea1487c2009ab8c1647789a9a