Fix Xcode 27 beta builds with correct Swift package deployment targets

Projects using Swift packages no longer fail to build with Xcode 27 beta because of outdated deployment targets. Swift 6.4 packages now default to iOS 15.0, macOS 12.0, watchOS 9.0, tvOS 15.0, and visionOS 1.0 floors, matching Xcode 27’s raised minimums.