Auto merge of #15495 - prampey:mql-borrow-error, r=jdm

Calling matchMedia during a MQL change event will not panic

<!-- Please describe your changes on the following line: -->
Calling matchMedia now leads to a new copy of MQL objects to prevent errors when borrowing references from MQL during an MQL change event.

---
<!-- 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] These changes fix #14967  (github issue number if applicable).

<!-- Either: -->
- [X] There are tests for these changes OR
- [x] These changes do not require tests because _____

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

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/15495)
<!-- Reviewable:end -->

tests/wpt/mozilla/meta/MANIFEST.json

@@ -13269,6 +13269,12 @@
      {}
     ]
    ],
+   "mozilla/mql_borrow.html": [
+    [
+     "/_mozilla/mozilla/mql_borrow.html",
+     {}
+    ]
+   ],
    "mozilla/navigator.html": [
     [
      "/_mozilla/mozilla/navigator.html",
@@ -25854,6 +25860,10 @@
    "5513229f79ab37de67eb4d60ea9dd23cd31d133f",
    "support"
   ],
+  "mozilla/mql_borrow.html": [
+   "f8f9adebe09f9473a52e5ec4f075540b10b32d7e",
+   "testharness"
+  ],
   "mozilla/navigator.html": [
    "939f453fecfb28a36cb93057382b56439b00b136",
    "testharness"