[content-visibility] Enable by default in stable

https://bugs.webkit.org/show_bug.cgi?id=269232
rdar://117156105

Reviewed by Aditya Keerthi.

Re-enable in stable releases now that most issues have been fixed.

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

Canonical link: https://commits.webkit.org/274491@main

Source/WTF/Scripts/Preferences/UnifiedWebPreferences.yaml

@@ -988,17 +988,17 @@ CSSContainmentEnabled:
 
 CSSContentVisibilityEnabled:
   type: bool
-  status: preview
+  status: stable
   category: css
   humanReadableName: "CSS Content Visibility"
   humanReadableDescription: "Enable CSS content-visibility"
   defaultValue:
     WebKitLegacy:
-      default: false
+      default: true
     WebKit:
-      default: false
+      default: true
     WebCore:
-      default: false
+      default: true
 
 CSSCounterStyleAtRuleImageSymbolsEnabled:
   type: bool