Fix cached ARCore-style static Objective-C xcframeworks behind dynamic ones

Google ARCore and similar static Objective-C xcframeworks with nested, prefix-self-importing headers (sitting behind a dynamic xcframework) can now be built when consumed from the binary cache. After #11472 hid module-map xcframework headers from search paths, builds of cached static-behind-dynamic deps started failing with 'ARCoreGARSession/GARTrackingState.h' file not found. The static-xcframework module-map mapper now also adds each matching slice’s Headers root to HEADER_SEARCH_PATHS, restoring the import path without reintroducing the module redefinition error in directly-linked xcframeworks.