Cherry-pick bf33b61. rdar://117595888

    Reenable requestIdleCallback by default in Apple's ports
    https://bugs.webkit.org/show_bug.cgi?id=262551

    Reviewed by Wenson Hsieh.

    The memory regression seen in PLUM3 has been fixed as of https://commits.webkit.org/268782@main.

    Re-enable requestIdleCallback in Apple's ports.

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

    Canonical link: https://commits.webkit.org/268800@main

Identifier: 267815.438@safari-7617.1.13.10-branch

Source/WTF/Scripts/Preferences/UnifiedWebPreferences.yaml

@@ -5375,14 +5375,15 @@ ReportingEnabled:
 
 RequestIdleCallbackEnabled:
   type: bool
-  status: preview
+  status: stable
   category: dom
   humanReadableName: "requestIdleCallback"
   humanReadableDescription: "Enable requestIdleCallback support"
   defaultValue:
     WebKitLegacy:
       default: false
     WebKit:
+      "USE(CF)": true
       default: false
     WebCore:
       default: false