Auto merge of #17763 - asajeffrey:script-worklets-pref, r=jdm

Placed worklets implementation behind a pref

<!-- Please describe your changes on the following line: -->

At the moment, worklets are always exposed, even though their spec is still a draft. This PR hides them behind a pref.

---
<!-- 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 #17680.
- [X] These changes do not require tests because the existing worklet tests do the job.

<!-- Also, please make sure that "Allow edits from maintainers" checkbox is checked, so that we can help you if you get stuck somewhere along the way.-->

<!-- 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/17763)
<!-- Reviewable:end -->

tests/wpt/mozilla/meta/MANIFEST.json

@@ -27241,7 +27241,7 @@
    "testharness"
   ],
   "mozilla/interfaces.html": [
-   "ffdc606aaf989ef8bcdecef8cef8764bbb2ae1b2",
+   "c884fee8603f93099ffd0acc30f0ab0cbee5b5f8",
    "testharness"
   ],
   "mozilla/interfaces.js": [

tests/wpt/mozilla/meta/mozilla/css-paint-api/__dir__.ini

@@ -0,0 +1 @@
+prefs: [dom.worklet.enabled:true]

tests/wpt/mozilla/meta/mozilla/worklets/__dir__.ini

@@ -0,0 +1 @@
+prefs: [dom.worklet.enabled:true]

tests/wpt/mozilla/tests/mozilla/interfaces.html

@@ -201,7 +201,6 @@ test_interfaces([
   "WebSocket",
   "Window",
   "Worker",
-  "Worklet",
   "XMLDocument",
   "XMLHttpRequest",
   "XMLHttpRequestEventTarget",