LibWeb: Traverse shadow boundaries when looking for focus candidates

This makes focusing input fields by clicking on them work.

Fixes #17801

Userland/Libraries/LibWeb/Page/EventHandler.cpp

@@ -385,7 +385,7 @@ bool EventHandler::handle_mousedown(CSSPixelPoint position, unsigned button, uns
             if (paintable->dom_node()) {
                 // See if we want to focus something.
                 bool did_focus_something = false;
-                for (auto candidate = node; candidate; candidate = candidate->parent()) {
+                for (auto candidate = node; candidate; candidate = candidate->parent_or_shadow_host()) {
                     if (candidate->is_focusable()) {
                         // When a user activates a click focusable focusable area, the user agent must run the focusing steps on the focusable area with focus trigger set to "click".
                         // Spec Note: Note that focusing is not an activation behavior, i.e. calling the click() method on an element or dispatching a synthetic click event on it won't cause the element to get focused.