Cached static-objc dependencies get the xcframework Headers root on search paths

Cached static Objective-C xcframeworks reached through a dynamic framework are compiled with the xcframework’s Headers root on HEADER_SEARCH_PATHS, alongside the module map’s own directory. Without this, nested snippets like ARCoreGARSession’s <Module/Sibling.h> cross-imports could not resolve. The fix keeps the library-products module cache working for SDKs that need both the headers and the module map to be discoverable.