Implement form-associated custom elements and their ElementInternals (#31980)

* FACEs work, setFormValue test is awful so now has _mozilla backup

* 1. Impl Validatable in ElementInternals instead of HTMLElement. 2. Reuse the code in Validatable trait. 3. The form associated custom element is not a customized built-in element.

* add some comments

* support readonly attribute and complete barred from constraint validation

* Addressed the code review comments

* Updated the legacy-layout results

* Fixed the WPT failures in ElementInternals-validation.html

* Addressed the code review comments

* Review suggestions

* Fixed silly mistakes and update the test result outside elementinternals

* update the test results

---------

Co-authored-by: Patrick Shaughnessy <pshaughn@comcast.net>
Co-authored-by: Martin Robinson <mrobinson@igalia.com>

tests/wpt/meta/custom-elements/ElementInternals-accessibility.html.ini

@@ -1,2 +1,144 @@
 [ElementInternals-accessibility.html]
-  expected: ERROR
+  [ElementInternals-accessibility]
+    expected: FAIL
+
+  [ariaDescribedByElements is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaFlowToElements is defined in ElementInternals]
+    expected: FAIL
+
+  [role is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaPosInSet is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaValueMax is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaDisabled is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaRoleDescription is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaValueMin is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaOrientation is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaLabel is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaMultiSelectable is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaExpanded is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaDetailsElements is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaColIndex is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaRowCount is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaBusy is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaChecked is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaControlsElements is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaAutoComplete is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaHasPopup is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaLevel is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaAtomic is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaErrorMessageElement is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaHidden is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaSort is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaRowSpan is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaRowIndex is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaPlaceholder is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaReadOnly is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaOwnsElements is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaActiveDescendantElement is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaColCount is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaRelevant is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaLive is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaValueNow is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaRequired is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaValueText is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaLabelledByElements is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaColSpan is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaModal is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaSelected is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaKeyShortcuts is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaCurrent is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaMultiLine is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaPressed is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaErrorMessageElements is defined in ElementInternals]
+    expected: FAIL
+
+  [ariaInvalid is defined in ElementInternals]
+    expected: FAIL