LibWeb: Expose HTMLSelectElement::options

Use the stub implementation of HTMLOptionsCollection to expose the
`option` children of `select` elements.

This fixes a JS error on openstreetmap.org, which occured when JQuery
code tried to access `options.length`:
https://github.com/jquery/jquery/blob/main/src/attributes/val.js#L121

Userland/Libraries/LibWeb/HTML/HTMLSelectElement.cpp

@@ -6,6 +6,7 @@
  */
 
 #include <LibWeb/HTML/HTMLFormElement.h>
+#include <LibWeb/HTML/HTMLOptionElement.h>
 #include <LibWeb/HTML/HTMLSelectElement.h>
 
 namespace Web::HTML {
@@ -19,4 +20,19 @@ HTMLSelectElement::~HTMLSelectElement()
 {
 }
 
+// https://html.spec.whatwg.org/multipage/form-elements.html#dom-select-options
+RefPtr<HTMLOptionsCollection> const& HTMLSelectElement::options()
+{
+    if (!m_options) {
+        m_options = HTMLOptionsCollection::create(*this, [](DOM::Element const& element) {
+            // https://html.spec.whatwg.org/multipage/form-elements.html#concept-select-option-list
+            // The list of options for a select element consists of all the option element children of
+            // the select element, and all the option element children of all the optgroup element children
+            // of the select element, in tree order.
+            return is<HTMLOptionElement>(element);
+        });
+    }
+    return m_options;
+}
+
 }