LibWeb: Make <input type=checkbox> fire click events when clicked :^)

This makes React react to checkboxes. Apparently they ignore the
"change" event in favor of "click" on checkboxes. This is a
compatibility hack for IE8.

Userland/Libraries/LibWeb/HTML/HTMLInputElement.h

@@ -43,6 +43,7 @@ public:
     bool enabled() const;
 
     void did_click_button(Badge<Layout::ButtonBox>);
+    void did_click_checkbox(Badge<Layout::CheckBox>);
 
     void did_edit_text_node(Badge<BrowsingContext>);