==== Background
`MentorWeightManager` relies on the `growthexperiments-mentorship-weight` user property only. User properties are the only place to store information about mentors with the wikitext list, however, when we switch to the structured list, we are able to store them on-wiki in a JSON blob. For that reason, when structured mentor list is enabled, `MentorWeightManager` doesn't need to be called at all.
==== Checklist
[ ] Ensure only `WikitextMentorProvider` and `ApiSetMentorWeight` use `MentorWeightManager`
[ ] Attempt to remove ApiSetMentorWeight (T314361). If not possible, ensure it does not call `MentorWeightManager` when structured mentor list is in use.
[ ] Throw when `MentorWeightManager` is used with incorrect provider (fatal error is easier to catch than a logic error when incorrect weights are used)