When running checks, we look to the existing problem check trackers and try to grab their ProblemCheck classes.
In some cases this is no longer in the problem check repository, e.g. when the check was part of a plugin that has been uninstalled.
In the case where the check was scheduled, this would lead to an error in one of the jobs
Previously the problem check registry simply looked at the subclasses of ProblemCheck. This was causing some confusion in environments where eager loading is not enabled, as the registry would appear empty as a result of the classes never being referenced (and thus never loaded.)
This PR changes the approach to a more explicit one. I followed other implementations (bookmarkable and hashtag autocomplete.) As a bonus, this now has a neat plugin entry point as well.
The build is broken due to some changes not being staged when I pushed the previous PR. The assertions that check that a job has been scheduled needs to be updated to reflect the new name.
Doing the following renames:
Jobs::ProblemChecks → Jobs::RunProblemChecks
Jobs::ProblemCheck → Jobs::RunProblemCheck
This is to disambiguate the ProblemCheck class name, ease fuzzy finding, and avoid needing to use :: in a bunch of places.
