LibWeb: Add an Internals method to dump the GC graph

Author: https://github.com/tcl3
Commit: 74940726d0
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/6689

Libraries/LibWeb/Internals/Internals.idl

@@ -57,6 +57,7 @@ interface Internals {
     readonly attribute boolean headless;
 
     DOMString dumpDisplayList();
+    DOMString dumpGCGraph();
 
     // Returns the shadow root of the element, if it has one, even if it's not normally accessible to JS.
     ShadowRoot? getShadowRoot(Element element);