Create related managers from generated managers (#580)

tests/typecheck/fields/test_related.yml

@@ -652,10 +652,18 @@
 
 -   case: related_manager_is_a_subclass_of_default_manager
     main: |
-        from myapp.models import User
-        reveal_type(User().orders)  # N: Revealed type is 'myapp.models.Order_RelatedManager'
+        from myapp.models import User, Order, Product
+        reveal_type(User().orders)  # N: Revealed type is 'myapp.models.User_Order_RelatedManager1'
         reveal_type(User().orders.get())  # N: Revealed type is 'myapp.models.Order*'
         reveal_type(User().orders.manager_method())  # N: Revealed type is 'builtins.int'
+        reveal_type(Order().products)  # N: Revealed type is 'myapp.models.Order_Product_RelatedManager1'
+        reveal_type(Order().products.get())  # N: Revealed type is 'myapp.models.Product*'
+        reveal_type(Order().products.queryset_method())  # N: Revealed type is 'builtins.int'
+        # TODO: realted manager support to use the same type for all related managers
+        if 1 == 2:
+            manager = User().products
+        else:
+            manager = Order().products  # E: Incompatible types in assignment (expression has type "Order_Product_RelatedManager1", variable has type "User_Product_RelatedManager1")
     installed_apps:
         - myapp
     files:
@@ -671,6 +679,46 @@
                 class Order(models.Model):
                     objects = OrderManager()
                     user = models.ForeignKey(to=User, on_delete=models.CASCADE, related_name='orders')
+                class ProductQueryset(models.QuerySet):
+                    def queryset_method(self) -> int:
+                        pass
+                ProductManager = models.Manager.from_queryset(ProductQueryset)
+                class Product(models.Model):
+                    objects = ProductManager()
+                    order = models.ForeignKey(to=Order, on_delete=models.CASCADE, related_name='products')
+                    user = models.ForeignKey(to=User, on_delete=models.CASCADE, related_name='products')
+
+-   case: related_manager_no_conflict_from_star_import
+    main: |
+        import myapp.models
+    installed_apps:
+        - myapp
+    files:
+        -   path: myapp/__init__.py
+        -   path: myapp/models/__init__.py
+            content: |
+                from myapp.models.a import *
+                # make sure generated related manager from address to user doesn't have
+                # the same name with related manager from profile to user
+                from myapp.models.b import *
+        -   path: myapp/models/a.py
+            content: |
+                from django.db import models
+                class Address(models.Model):
+                    pass
+        -   path: myapp/models/b.py
+            content: |
+                from django.db import models
+                from .a import Address
+                class Profile(models.Model):
+                    pass
+                class UserQuerySet(models.QuerySet):
+                    pass
+                UserManager = models.Manager.from_queryset(UserQuerySet)
+                class User(models.Model):
+                    address = models.ForeignKey(Address, on_delete=models.CASCADE)
+                    profile = models.ForeignKey(Profile, on_delete=models.CASCADE)
+                    objects = UserManager()
 
 -   case: many_to_many_field_can_be_used_in_alias
     main: |