gdebugcontroller: Add documentation and tests
See the commit messages. This drops one of the APIs added earlier, so needs to be reviewed and merged before 2.71.2 (the API freeze).
Fixes: #1190 (closed)
See the commit messages. This drops one of the APIs added earlier, so needs to be reviewed and merged before 2.71.2 (the API freeze).
Fixes: #1190 (closed)