Implement IDREF element reflection

https://bugs.webkit.org/show_bug.cgi?id=196843

Reviewed by Ryosuke Niwa.

Enable AriaReflectionForElementReferencesEnabled experimental flag by
default.

* Source/WTF/Scripts/Preferences/WebPreferencesExperimental.yaml:

Canonical link: https://commits.webkit.org/252590@main

Source/WTF/Scripts/Preferences/WebPreferencesExperimental.yaml

@@ -72,11 +72,11 @@ AriaReflectionForElementReferencesEnabled:
   humanReadableDescription: "Enable ARIA reflection for attributes that refer to elements"
   defaultValue:
     WebKitLegacy:
-      default: false
+      default: true
     WebKit:
-      default: false
+      default: true
     WebCore:
-      default: false
+      default: true
 
 AspectRatioEnabled:
   type: bool