ARCore-style nested static Objective-C xcframeworks build correctly when cached

Projects that cache static Objective-C xcframeworks with a nested header layout (module map and public headers under a Headers// subdirectory, with prefixed self-imports such as #import <ARCoreGARSession/GARAnchor.h>) now build successfully through the binary cache behind a dynamic framework. The mapper detects this nested layout and points -fmodule-map-file at the xcframework’s own module map and HEADER_SEARCH_PATHS at the Headers root, so the module is defined exactly once and the prefix imports resolve. This unblocks caching xcframeworks like ARCoreGARSession and ARCoreGeospatial, which previously failed with “file not found” or “import of shadowed module” errors. Flat layouts are unchanged.