[view-transitions] Enable by default

https://bugs.webkit.org/show_bug.cgi?id=269632
rdar://123128491

Reviewed by Simon Fraser.

Most demos now function to a decent level as of #26175.

Remaining functionality is polish on top of the current work.

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

Canonical link: https://commits.webkit.org/276426@main

Source/WTF/Scripts/Preferences/UnifiedWebPreferences.yaml

@@ -7136,16 +7136,16 @@ ViewGestureDebuggingEnabled:
 ViewTransitionsEnabled:
   type: bool
   category: animation
-  status: testable
+  status: stable
   humanReadableName: "View Transitions"
   humanReadableDescription: "Enable the View Transitions API"
   defaultValue:
     WebKitLegacy:
-      default: false
+      default: true
     WebKit:
-      default: false
+      default: true
     WebCore:
-      default: false
+      default: true
 
 VisibleDebugOverlayRegions:
   type: uint32_t