Fix Swift package deployment targets for Xcode 27 beta

Xcode 27 beta raises the minimum supported deployment target for Swift package targets, so packages that declared older floors (e.g., iOS 13.0) previously caused compilation errors. Tuist now chooses Swift package deployment target floors based on the Swift compiler era, matching the newer Xcode behavior. Swift 5.9 packages keep the old iOS 12.0 minimum, while Swift 6.4 (used by Xcode 27 beta) now defaults to iOS 15.0, macOS 12.0, watchOS 9.0, tvOS 15.0, and visionOS 1.0. This fixes builds that failed with ‘deployment target … is set to … but the range of supported deployment target versions is …’ errors after upgrading to Xcode 27 beta.