Fix cached static-ObjC xcframeworks behind dynamic xcframeworks (ARCore) failing to build

Projects that depend on a static Objective-C xcframework reached behind a dynamic xcframework (for example Google’s ARCore) and pull it from the binary cache no longer fail with 'ARCoreGARSession/GARTrackingState.h' file not found and could not build Objective-C module 'ARCoreGARSession'. Tuist now adds the xcframework’s Headers root to HEADER_SEARCH_PATHS for each matching slice, so headers that re-import siblings with their framework prefix resolve correctly. Flat-layout xcframeworks (like GoogleMaps) and directly-linked xcframeworks behave as before.