Module-map xcframework headers excluded from search paths

Targets depending on a precompiled xcframework that ships a module.modulemap no longer fail with Redefinition of module 'X'. Tuist now skips adding those Headers directories to HEADER_SEARCH_PATHS when the xcframework ships a module map, leaving Xcode’s ProcessXCFramework include/ copy to provide the right one. Module-map-less xcframeworks (cached Swift/library products) keep their headers.