Improve the ArcanistInfrastructureTestCase unit tests such that they will fail if any of the following conditions are satisfied:
- A symbol referenced in the __phutil_library_map__.php file no longer exists.
- A symbol exists in the library but is not referenced within the __phutil_library_map__.php file.
- A symbol extends from a different parent symbol than that declared in the __phutil_library_map.php file.