[utils] Don't attempt to coerce JS strings to numbers in js_to_json (#26851)

The current logic in `js_to_json` tries to rewrite octal/hex numbers to
decimal. However, when the logic actually happens the `"` or `'` have
already been trimmed off. This causes what were originally strings, that
happen to look like octal/hex numbers, to get rewritten to decimal and
returned as a number rather than a string.

In practive something like:

```js
{
  "0x40": "foo",
  "040": "bar",
}
```

would get rewritten as:

```json
{
  64: "foo",
  32: "bar
}
```

This is problematic since this isn't valid JSON as you cannot have
non-string keys.

test/test_utils.py

@@ -994,6 +994,12 @@ class TestUtil(unittest.TestCase):
         on = js_to_json('{42:4.2e1}')
         self.assertEqual(json.loads(on), {'42': 42.0})
 
+        on = js_to_json('{ "0x40": "0x40" }')
+        self.assertEqual(json.loads(on), {'0x40': '0x40'})
+
+        on = js_to_json('{ "040": "040" }')
+        self.assertEqual(json.loads(on), {'040': '040'})
+
     def test_js_to_json_malformed(self):
         self.assertEqual(js_to_json('42a1'), '42"a1"')
         self.assertEqual(js_to_json('42a-1'), '42"a"-1')