Fix module map copy so cached builds can overwrite read-only outputs

Generated projects with SwiftPM dependencies that carry custom module maps (such as Objective-C packages or swift-atomics shims) now build successfully when Xcode compilation caching is enabled. The “Copy Module Map” script phase appended to framework targets now uses cp -f instead of plain cp, so it can overwrite the read-only module map files that the CAS materializes. This unblocks Xcode Cache adoption for projects that depend on such packages.