Cached static Objective-C xcframeworks (ARCore-style) build correctly

Static Objective-C xcframeworks with a module map that lives next to the headers, including ARCore-style nested layouts with Headers/<ModuleName>/, are now consumed correctly through the binary cache. The mapper distinguishes the nested case (use the xcframework’s own module map and the Headers root as the search path) from the flat case (derived module map + prefix-stripped umbrella, unchanged). Previously these dependencies failed with 'ARCoreGARSession/GARTrackingState.h' file not found or import of shadowed module 'GARAnchor', depending on the RC.