[lldb] Rename some register type classes (#213684) Follow up to #196960. So that when more types are added, the hierarchy is clear. RegisterType -> RegisterTypeEnum -> RegisterTypeFlags (in future also...) -> RegisterTypeUnion -> RegisterTypeVector Renamed and moved the test file as it will cover all the classes derived from RegisterType. GitOrigin-RevId: f80ea9af1f29cc202d0b6ba077e79769b6f6184c