LibWeb: Add NavigateEvent.sourceElement

Corresponds to:
- https://github.com/whatwg/html/pull/10898
- https://github.com/whatwg/html/pull/10971

I've also updated the imported WPT test as it's been recently changed to
account for 10898 being merged.

Libraries/LibWeb/HTML/NavigateEvent.idl

@@ -19,6 +19,7 @@ interface NavigateEvent : Event {
     readonly attribute DOMString? downloadRequest;
     readonly attribute any info;
     readonly attribute boolean hasUAVisualTransition;
+    readonly attribute Element? sourceElement;
 
     undefined intercept(optional NavigationInterceptOptions options = {});
     undefined scroll();
@@ -35,6 +36,7 @@ dictionary NavigateEventInit : EventInit {
     DOMString? downloadRequest = null;
     any info;
     boolean hasUAVisualTransition = false;
+    Element? sourceElement = null;
 };
 
 dictionary NavigationInterceptOptions {