LibWeb: Port {Mouse,UI,Wheel,}Event to new String

This ports MouseEvent, UIEvent, WheelEvent, and Event to new String.
They all had a dependency to T::create() in
WebDriverConnection::fire_an_event() and therefore had to be ported in
the same commit.

Userland/Libraries/LibWeb/UIEvents/MouseEvent.idl

@@ -1,5 +1,5 @@
 // https://w3c.github.io/uievents/#mouseevent
-[Exposed=Window]
+[Exposed=Window, UseNewAKString]
 interface MouseEvent : UIEvent {
 
     readonly attribute double offsetX;