Summary: Part of #24875, adds a spec for ExceptionsManager ## Changelog [General] [Added] - TM Add spec for ExceptionsManager Pull Request resolved: https://github.com/facebook/react-native/pull/24900 Reviewed By: fkgozali Differential Revision: D15434006 Pulled By: RSNara fbshipit-source-id: 1a505744a84c0c4ac3a9fac6c91a391fbd8a9f46