Fixed #21961 -- Added support for database-level delete options for ForeignKey.

Thanks Simon Charette for pair programming.

Co-authored-by: Nick Stefan <NickStefan12@gmail.com>
Co-authored-by: Akash Kumar Sen <71623442+Akash-Kumar-Sen@users.noreply.github.com>
Co-authored-by: Simon Charette <charette.s@gmail.com>

tests/migrations/test_writer.py

@@ -971,6 +971,23 @@ class WriterTests(SimpleTestCase):
             ("('models.Model', {'from django.db import models'})", set()),
         )
 
+    def test_database_on_delete_serializer_value(self):
+        db_level_on_delete_options = [
+            models.DB_CASCADE,
+            models.DB_SET_DEFAULT,
+            models.DB_SET_NULL,
+        ]
+        for option in db_level_on_delete_options:
+            self.assertSerializedEqual(option)
+            self.assertSerializedResultEqual(
+                MigrationWriter.serialize(option),
+                (
+                    f"('django.db.models.deletion.{option.__name__}', "
+                    "{'import django.db.models.deletion'})",
+                    set(),
+                ),
+            )
+
     def test_simple_migration(self):
         """
         Tests serializing a simple migration.