LibWeb/HTML: Add fastpath to skip selectedness update on option insert

This extends the optimization introduced in the previous commit to
also apply to the inserted steps for an option element. This makes
the test:

https://wpt.live/html/select/options-length-too-large.html

Go from not ever completing due to how slow it was to running, to
finishing in 800ms on my PC :^)

Libraries/LibWeb/HTML/HTMLSelectElement.h

@@ -98,6 +98,8 @@ public:
 
     void update_inner_text_element(Badge<HTMLOptionElement>);
 
+    bool can_skip_selectedness_update_for_inserted_option(HTMLOptionElement const&) const;
+
 private:
     HTMLSelectElement(DOM::Document&, DOM::QualifiedName);