Add tvOS 16 and visionOS 1 to the supported platforms.
XibKit is UIKit-based and ships no bundled resources, so it compiles unchanged on both platforms. Verified with xcodebuild build for iOS, tvOS and visionOS.
The test suite remains iOS-only: its xib fixtures are targetRuntime="iOS.CocoaTouch", which tvOS rejects. This affects the test target only, not the shipped library.
tvOS is set to 16 rather than 15 because the SpryKit test dependency requires it.