LibWeb: Implement the PointerEvent interface

As defined in: https://w3c.github.io/pointerevents

With the exception of the getCoalescedEvents and getPredictedEvents
APIs.

There are still many other parts of that spec (such as the event
handlers) left to implement, but this does get us at least some of the
way.

Userland/Libraries/LibWeb/HTML/HTMLElement.cpp

@@ -31,6 +31,7 @@
 #include <LibWeb/UIEvents/EventNames.h>
 #include <LibWeb/UIEvents/FocusEvent.h>
 #include <LibWeb/UIEvents/MouseEvent.h>
+#include <LibWeb/UIEvents/PointerEvent.h>
 #include <LibWeb/WebIDL/DOMException.h>
 #include <LibWeb/WebIDL/ExceptionOr.h>