firebase-ios-sdk

App Distribution: Implement code hash generation and verification (#5432)

Add initial code hash generation implementation

Generate a code hash by getting the architecture and uuids for the app, sorting the list lexicographically by architecture, concatenating the uuids and generate a hash using SHA1 (for legacy purposes). We then use the code hash to verify against a hash returned from the server to determine whether the current running version is the latest version.