LibWeb+UI: Add internals API to set browser zoom

Author: https://github.com/InvalidUsernameException
Commit: 5cc9a5802d
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/2982
Reviewed-by: https://github.com/AtkinsSJ

Libraries/LibWeb/Internals/Internals.idl

@@ -45,5 +45,7 @@ interface Internals {
     DOMString getComputedLabel(Element element);
     unsigned short getEchoServerPort();
 
+    undefined setBrowserZoom(double factor);
+
     readonly attribute boolean headless;
 };