LibWeb/URLPattern: Add initial stub for URLPattern interface

Author: https://github.com/shannonbooth
Commit: d4649db55e
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/3224
Reviewed-by: https://github.com/AtkinsSJ ✅

Libraries/LibWeb/Forward.h

@@ -796,6 +796,10 @@ class TextEvent;
 class UIEvent;
 }
 
+namespace Web::URLPattern {
+class URLPattern;
+}
+
 namespace Web::DOMURL {
 class DOMURL;
 class URLSearchParams;