Merge changes from topic "cherrypicker-L94400030000731002:N23400030012047507" into main

* changes:
  [nearby] Returns error code for startBroadcast if there is an existing broadcast
  [nearby] Update README
  [nearby] Unregister broadcast listener in death
  [nearby] Add CredentialElement class
  [nearby][framework] Sync DataElement value with spec
  Fix NearbyConfigurationTest.
  Catches illegal argument exception thrown by LE advertiser