Add safety-checking hook to 'tryRunMigrationsWithEditUpdate'

[alexfmpe]

No description provided.

[alexfmpe]

I think we ended up needing the hook to be Schema -> [WithPriority Edit] -> [WithPriority Edit] so we could reason about the intended schema (current one is available by querying the database) and not just reverse engineer intent from the diff.
e.g. we might be expecting a rename, and be able to confirm it on the schemas, but the diff will have a pair of unrelated column delete/add.
This was kept as a draft until I was more confident in the change since it was a breaking one (we could always come up with a new name)

[alexfmpe]

I think we ended up needing the hook to be Schema -> [WithPriority Edit] -> [WithPriority Edit]

Should 9d8d8af be cherry picked here?