LibWeb: Evaluate @media rules

We now evaluate the conditions of `@media` rules at the same point in
the HTML event loop as evaluation of `MediaQueryList`s. This is not
strictly to spec, but since the spec doesn't actually say when to do
this, it seems to make the most sense. In any case, it works! :^)

Userland/Libraries/LibWeb/DOM/Document.cpp

@@ -1156,6 +1156,11 @@ void Document::evaluate_media_queries_and_report_changes()
             media_query_list->dispatch_event(event);
         }
     }
+
+    // Also not in the spec, but this is as good a place as any to evaluate @media rules!
+    for (auto& style_sheet : style_sheets().sheets()) {
+        style_sheet.evaluate_media_queries(window());
+    }
 }
 
 }