Add support for inline from_queryset in model classes (#1045)

* Add support for inline from_queryset in model classes

This adds support for calling <Manager>.from_queryset(<QuerySet>)()
inline in models, for example like this:

    class MyModel(models.Model):
        objects = MyManager.from_queryset(MyQuerySet)()

This is done by inspecting the class body in the transform_class_hook

* Fix missing methods on copied manager

* Add test and other minor tweaks

* Always create manager at module level

When the manager is added at the class level, which happened when it was
created inline in the model body, it's not possible to retrieve the
manager again based on fullname. That lead to problems with inheritance
and the default manager.

tests/typecheck/fields/test_related.yml

@@ -678,7 +678,6 @@
                     def custom(self) -> None:
                         pass
 
-                # Note, that we cannot resolve dynamic calls for custom managers:
                 class Transaction(models.Model):
                     objects = BaseManager.from_queryset(TransactionQuerySet)
                     def test(self) -> None:
@@ -689,9 +688,8 @@
                 class TransactionLog(models.Model):
                     transaction = models.ForeignKey(Transaction, on_delete=models.CASCADE)
     out: |
-        myapp/models:9: error: `.from_queryset` called from inside model class body
-        myapp/models:11: note: Revealed type is "django.db.models.manager.RelatedManager[myapp.models.TransactionLog]"
-        myapp/models:13: note: Revealed type is "Any"
+        myapp/models:10: note: Revealed type is "django.db.models.manager.RelatedManager[myapp.models.TransactionLog]"
+        myapp/models:12: note: Revealed type is "Any"
 
 
 -   case: resolve_primary_keys_for_foreign_keys_with_abstract_self_model