Fixed #35859 -- Added background Tasks framework interface.

This work implements what was defined in DEP 14
(https://github.com/django/deps/blob/main/accepted/0014-background-workers.rst).

Thanks to Raphael Gaschignard, Eric Holscher, Ran Benita, Sarah Boyce,
Jacob Walls, and Natalia Bidart for the reviews.

tests/utils_tests/test_json.py

@@ -0,0 +1,46 @@
+import json
+from collections import UserList, defaultdict
+from datetime import datetime
+from decimal import Decimal
+
+from django.test import SimpleTestCase
+from django.utils.json import normalize_json
+
+
+class JSONNormalizeTestCase(SimpleTestCase):
+    def test_converts_json_types(self):
+        for test_case, expected in [
+            (None, "null"),
+            (True, "true"),
+            (False, "false"),
+            (2, "2"),
+            (3.0, "3.0"),
+            (1e23 + 1, "1e+23"),
+            ("1", '"1"'),
+            (b"hello", '"hello"'),
+            ([], "[]"),
+            (UserList([1, 2]), "[1, 2]"),
+            ({}, "{}"),
+            ({1: "a"}, '{"1": "a"}'),
+            ({"foo": (1, 2, 3)}, '{"foo": [1, 2, 3]}'),
+            (defaultdict(list), "{}"),
+            (float("nan"), "NaN"),
+            (float("inf"), "Infinity"),
+            (float("-inf"), "-Infinity"),
+        ]:
+            with self.subTest(test_case):
+                normalized = normalize_json(test_case)
+                # Ensure that the normalized result is serializable.
+                self.assertEqual(json.dumps(normalized), expected)
+
+    def test_bytes_decode_error(self):
+        with self.assertRaisesMessage(ValueError, "Unsupported value"):
+            normalize_json(b"\xff")
+
+    def test_encode_error(self):
+        for test_case in [self, any, object(), datetime.now(), set(), Decimal("3.42")]:
+            with (
+                self.subTest(test_case),
+                self.assertRaisesMessage(TypeError, "Unsupported type"),
+            ):
+                normalize_json(test_case)