* Fix many version checks to be based on Xcode version instead of iOS version.
* Added/fixed a few expected values according to platform version to match behavior in older macOS versions.
Largely related to somewhat recent frameworks/API additions to XM
ExternalAccessory was added to macOS 10.13 (Xcode9) and can't be run before that (including on the jenkins sierra bots). Also enable that test on tvOS (which added support in Xcode8)