Notify user when connecting as follower fails (#19477)
Replaces #19454
Replaces #19467
Fixes #19103
Summary of the issue:
Users are not notified when connecting as the controlled computer (follower) fails. Only the leader connection errors are shown to users.
Description of user facing changes:
Users will now see an error message when connection as the controlled computer fails, just like when connecting as the controlling computer.
Description of developer facing changes:
None.
Description of development approach:
Made follower connection error handling consistent with leader connection by adding the missing event handler and user notification.
Added onConnectAsFollowerFailed method in client.py to handle follower connection failures;
Registered transportConnectionFailed event handler for follower transport;
Added cleanup for event handlers in disconnectAsFollower method.
