LibJS: Handle both const and non-const Ts in Handle<T>::create()

Again, the const-ness only really involves Heap-internal metadata, so
the callers shouldn't care about mutations here.

Userland/Libraries/LibJS/Heap/Handle.h

@@ -46,7 +46,7 @@ public:
 
     static Handle create(T* cell)
     {
-        return Handle(adopt_ref(*new HandleImpl(cell)));
+        return Handle(adopt_ref(*new HandleImpl(const_cast<RemoveConst<T>*>(cell))));
     }
 
     Handle(T* cell)

Userland/Libraries/LibWeb/DOM/Document.cpp

@@ -2121,7 +2121,7 @@ Vector<JS::Handle<HTML::BrowsingContext>> Document::list_of_descendant_browsing_
     //       of this document's browsing context.
     if (browsing_context()) {
         browsing_context()->for_each_in_subtree([&](auto& context) {
-            list.append(JS::make_handle(const_cast<HTML::BrowsingContext&>(context)));
+            list.append(JS::make_handle(context));
             return IterationDecision::Continue;
         });
     }

Userland/Libraries/LibWeb/Fetch/Fetching/Fetching.cpp

@@ -838,7 +838,7 @@ WebIDL::ExceptionOr<JS::NonnullGCPtr<PendingResponse>> http_fetch(JS::Realm& rea
             // NOTE: Step 2 is performed in pending_preflight_response's load callback below.
         }
 
-        auto fetch_main_content = [request = JS::make_handle(request), realm = JS::make_handle(realm), fetch_params = JS::make_handle(const_cast<Infrastructure::FetchParams&>(fetch_params))]() -> WebIDL::ExceptionOr<JS::NonnullGCPtr<PendingResponse>> {
+        auto fetch_main_content = [request = JS::make_handle(request), realm = JS::make_handle(realm), fetch_params = JS::make_handle(fetch_params)]() -> WebIDL::ExceptionOr<JS::NonnullGCPtr<PendingResponse>> {
             // 2. If request’s redirect mode is "follow", then set request’s service-workers mode to "none".
             // NOTE: Redirects coming from the network (as opposed to from a service worker) are not to be exposed to a
             //       service worker.

Userland/Libraries/LibWeb/Fetch/Fetching/PendingResponse.cpp

@@ -52,11 +52,11 @@ void PendingResponse::resolve(JS::NonnullGCPtr<Infrastructure::Response> respons
         run_callback();
 }
 
-void PendingResponse::run_callback() const
+void PendingResponse::run_callback()
 {
     VERIFY(m_callback);
     VERIFY(m_response);
-    Platform::EventLoopPlugin::the().deferred_invoke([strong_this = JS::make_handle(const_cast<PendingResponse&>(*this))] {
+    Platform::EventLoopPlugin::the().deferred_invoke([strong_this = JS::make_handle(*this)] {
         strong_this->m_callback(*strong_this->m_response);
         strong_this->m_request->remove_pending_response({}, *strong_this.ptr());
     });

Userland/Libraries/LibWeb/Fetch/Fetching/PendingResponse.h

@@ -35,7 +35,7 @@ private:
 
     virtual void visit_edges(JS::Cell::Visitor&) override;
 
-    void run_callback() const;
+    void run_callback();
 
     Callback m_callback;
     JS::NonnullGCPtr<Infrastructure::Request> m_request;

Userland/Libraries/LibWeb/HTML/HTMLSelectElement.cpp

@@ -84,13 +84,13 @@ Vector<JS::Handle<HTMLOptionElement>> HTMLSelectElement::list_of_options() const
     // and all the option element children of all the optgroup element children of the select element, in tree order.
     Vector<JS::Handle<HTMLOptionElement>> list;
 
-    for_each_child_of_type<HTMLOptionElement>([&](HTMLOptionElement const& option_element) {
-        list.append(JS::make_handle(const_cast<HTMLOptionElement&>(option_element)));
+    for_each_child_of_type<HTMLOptionElement>([&](HTMLOptionElement& option_element) {
+        list.append(JS::make_handle(option_element));
     });
 
     for_each_child_of_type<HTMLOptGroupElement>([&](HTMLOptGroupElement const& optgroup_element) {
-        optgroup_element.for_each_child_of_type<HTMLOptionElement>([&](HTMLOptionElement const& option_element) {
-            list.append(JS::make_handle(const_cast<HTMLOptionElement&>(option_element)));
+        optgroup_element.for_each_child_of_type<HTMLOptionElement>([&](HTMLOptionElement& option_element) {
+            list.append(JS::make_handle(option_element));
         });
     });