LibWeb+LibJS: Make the EventTarget hierarchy (incl. DOM) GC-allocated

This is a monster patch that turns all EventTargets into GC-allocated
PlatformObjects. Their C++ wrapper classes are removed, and the LibJS
garbage collector is now responsible for their lifetimes.

There's a fair amount of hacks and band-aids in this patch, and we'll
have a lot of cleanup to do after this.

Userland/Libraries/LibWeb/HTML/HTMLOptionElement.h

@@ -12,10 +12,9 @@
 namespace Web::HTML {
 
 class HTMLOptionElement final : public HTMLElement {
-public:
-    using WrapperType = Bindings::HTMLOptionElementWrapper;
+    WEB_PLATFORM_OBJECT(HTMLOptionElement, HTMLElement);
 
-    HTMLOptionElement(DOM::Document&, DOM::QualifiedName);
+public:
     virtual ~HTMLOptionElement() override;
 
     bool selected() const { return m_selected; }
@@ -33,6 +32,8 @@ private:
     friend class Bindings::OptionConstructor;
     friend class HTMLSelectElement;
 
+    HTMLOptionElement(DOM::Document&, DOM::QualifiedName);
+
     void parse_attribute(FlyString const& name, String const& value) override;
     void did_remove_attribute(FlyString const& name) override;
 
@@ -46,3 +47,5 @@ private:
 };
 
 }
+
+WRAPPER_HACK(HTMLOptionElement, Web::HTML)