LibJS: Make Cell::initialize() return void

Stop worrying about tiny OOMs.

Work towards #20405

Userland/Libraries/LibWeb/HTML/HTMLBodyElement.h

@@ -32,7 +32,7 @@ private:
     // ^DOM::Node
     virtual bool is_html_body_element() const override { return true; }
 
-    virtual JS::ThrowCompletionOr<void> initialize(JS::Realm&) override;
+    virtual void initialize(JS::Realm&) override;
 
     // ^HTML::GlobalEventHandlers
     virtual EventTarget& global_event_handlers_to_event_target(FlyString const& event_name) override;