Notify user when connecting as follower fails

[tareh7z]

Link to issue number:

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.

Testing strategy:

Tested manually.

Known issues with pull request:

None known.

Code Review Checklist:

• Documentation:
  • Change log entry
  • User Documentation
  • Developer / Technical Documentation
  • Context sensitive help for GUI changes
• Testing:
  • Unit tests
  • System (end to end) tests
  • Manual testing
• UX of all users considered:
  • Speech
  • Braille
  • Low Vision
  • Different web browsers
  • Localization in other languages / culture than English
• API is compatible with existing add-ons.
• Security precautions taken.