LibWeb: Fix select element state update in three ways

1. We were not propagating selectedness updates from option to select
   if the option was inside an optgroup.

2. When two or more options were selected, we were always favoring the
   last one in tree order, instead of the last one that got checked.

3. We were neglecting to return in the `display size is 1` case when
   all elements were disabled.

This was covered by some of the :has() selector tests. :^)

Userland/Libraries/LibWeb/HTML/HTMLSelectElement.cpp

@@ -558,7 +558,7 @@ void HTMLSelectElement::update_inner_text_element()
 }
 
 // https://html.spec.whatwg.org/multipage/form-elements.html#selectedness-setting-algorithm
-void HTMLSelectElement::update_selectedness()
+void HTMLSelectElement::update_selectedness(JS::GCPtr<HTML::HTMLOptionElement> last_selected_option)
 {
     if (has_attribute(AttributeNames::multiple))
         return;
@@ -581,9 +581,10 @@ void HTMLSelectElement::update_selectedness()
                 if (!option_element->disabled()) {
                     option_element->set_selected_internal(true);
                     update_inner_text_element();
-                    return;
+                    break;
                 }
             }
+            return;
         }
     }
 
@@ -601,6 +602,8 @@ void HTMLSelectElement::update_selectedness()
         // then set the selectedness of all but the last option element with its selectedness set to true
         // in the list of options in tree order to false.
         for (auto const& option_element : list_of_options()) {
+            if (option_element == last_selected_option)
+                continue;
             if (number_of_selected == 1) {
                 break;
             }