Removed usage of deprecated django.utils.importlib.
Fixed #22750, #22248: Model renaming now also alters field FKs
Optimize is_protected_type slightly (used by force_text, which is used basically everywhere)
Gave unique names to SpatialRefSysModels.

Prevented clashes in the app registry.

Fixed #22790. Thanks timo for the report.
Fixed #22777: Add dependency on through for autodetected M2M adds