Add the xcframework Headers root for cached static-Objective-C behind-dynamic dependencies

When a static Objective-C xcframework is reached behind a dynamic framework through the binary cache, Tuist adds the xcframework slice’s Headers root to the consumer’s HEADER_SEARCH_PATHS in addition to the module map’s own directory. This restores the path that prefix-form <Module/Header.h> cross-imports rely on (the same situation as Google’s ARCore ARCoreGARSession), without reintroducing a second discoverable module map.