Refs #16043 -- Refactored internal fields value cache.

* Removed all hardcoded logic for _{fieldname}_cache.
* Added an internal API for interacting with the field values cache.

Thanks carljm and MarkusH for support.

tests/foreign_object/models/article.py

@@ -10,9 +10,9 @@ class ArticleTranslationDescriptor(ForwardManyToOneDescriptor):
     def __set__(self, instance, value):
         if instance is None:
             raise AttributeError("%s must be accessed via instance" % self.field.name)
-        setattr(instance, self.cache_name, value)
+        self.field.set_cached_value(instance, value)
         if value is not None and not self.field.remote_field.multiple:
-            setattr(value, self.field.related.get_cache_name(), instance)
+            self.field.remote_field.set_cached_value(value, instance)
 
 
 class ColConstraint: