Auto merge of #18317 - cbrewster:custom_elements_enable, r=jdm

Enable Custom Elements by Default

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

---
<!-- 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 #9372 (github issue number if applicable).

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- [ ] There are tests for these changes OR
- [X] These changes do not require tests because enabling pref flag.

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resources/prefs.json

@@ -3,7 +3,7 @@
   "dom.bluetooth.testing.enabled": false,
   "dom.canvas-text.enabled": false,
   "dom.compositionevent.enabled": false,
-  "dom.customelements.enabled": false,
+  "dom.customelements.enabled": true,
   "dom.forcetouch.enabled": false,
   "dom.gamepad.enabled": false,
   "dom.mouseevent.which.enabled": false,

tests/wpt/metadata/custom-elements/__dir__.ini

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

tests/wpt/metadata/custom-elements/attribute-changed-callback.html.ini

@@ -1,5 +0,0 @@
-[attribute-changed-callback.html]
-  type: testharness
-  [Custom Elements: attributeChangedCallback]
-    expected: FAIL
-

tests/wpt/metadata/fetch/api/cors/cors-preflight.any.js.ini

@@ -21,6 +21,7 @@
   [CORS [PUT\] [several headers\], server allows]
     expected: FAIL
 
+
 [cors-preflight.any.worker.html]
   type: testharness
   [CORS [PATCH\], server allows]
@@ -43,3 +44,4 @@
 
   [CORS [PUT\] [several headers\], server allows]
     expected: FAIL
+

tests/wpt/mozilla/meta/MANIFEST.json

@@ -27292,7 +27292,7 @@
    "testharness"
   ],
   "mozilla/interfaces.html": [
-   "48028c5a9b401bab52a155c8820140a65dbc2f11",
+   "a7ed38b6069caffd87d9573978e6ef9938d87753",
    "testharness"
   ],
   "mozilla/interfaces.js": [

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

@@ -43,6 +43,7 @@ test_interfaces([
   "DOMRect",
   "DOMRectReadOnly",
   "Comment",
+  "CustomElementRegistry",
   "CustomEvent",
   "Document",
   "DocumentFragment",