Fixed #28884 -- Fixed crash on SQLite when renaming a field in a model referenced by a ManyToManyField.

Introspected database constraints instead of relying on _meta.related_objects
to determine whether or not a table or a column is referenced on rename
operations.

This has the side effect of ignoring both db_constraint=False and virtual
fields such as GenericRelation which aren't backend by database level
constraints and thus shouldn't prevent the rename operations from being
performed in a transaction.

Regression in 095c1aaa.

Thanks Tim for the additional tests and edits, and Mariusz for the review.