servo: Merge #14092 - Sort check on JSON (from kivikakk:sort-check); r=Wafflespeanut

<!-- Please describe your changes on the following line: -->
Check that JSON keys are ordered, and that there's no duplicates (for `resources/prefs.json` and `resources/package-prefs.json`).

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x]  🆕 `./mach test-tidy --self-test` does not report any errors
- [x] These changes fix #12283

<!-- Either: -->
- [x] There are tests for these changes 🎉

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

Source-Repo: https://github.com/servo/servo
Source-Revision: 94d0c485e10138e0d5b2bd8b41b6a922a22a059f

servo/python/tidy/servo_tidy_tests/test_tidy.py

@@ -171,6 +171,12 @@ class CheckTidiness(unittest.TestCase):
         self.assertEqual('Duplicated Key (the_duplicated_key)', errors.next()[2])
         self.assertNoMoreErrors(errors)
 
+    def test_json_with_unordered_keys(self):
+        tidy.config["check-ordered-json-keys"].append('python/tidy/servo_tidy_tests/unordered_key.json')
+        errors = tidy.collect_errors_for_files(iterFile('unordered_key.json'), [tidy.check_json], [], print_text=False)
+        self.assertEqual('Unordered key (found b before a)', errors.next()[2])
+        self.assertNoMoreErrors(errors)
+
     def test_lock(self):
         errors = tidy.collect_errors_for_files(iterFile('duplicated_package.lock'), [tidy.check_lock], [], print_text=False)
         msg = """duplicate versions for package "test"

servo/python/tidy/servo_tidy_tests/unordered_key.json

@@ -0,0 +1,7 @@
+{
+    "key": "value",
+    "other_key": {
+        "b": 1,
+        "a": 2
+    }
+}