- Changes the `alreadyChecked` flag of AbstractChangeDetector to a new `state` flag.
- Changes all checks of alreadyChecked to check that the state is NeverChecked.
- Set state to Errored if an error is thrown during detection.
- Skip change detection for a detector and its children when the state is Errored.
- Add a test to validate this fixes issue #4323.
Closes#4953