LibJS: Generalize PromiseAllResolveElementFunction common functionality

The element-resolving functions on the Promise constructor are all very
similar. To prepare for more of these functions to be implemented, break
out common parts into a base class.

Userland/Libraries/LibJS/Runtime/PromiseResolvingElementFunctions.cpp

@@ -0,0 +1,75 @@
+/*
+ * Copyright (c) 2021, Tim Flynn <trflynn89@pm.me>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibJS/Runtime/AbstractOperations.h>
+#include <LibJS/Runtime/Array.h>
+#include <LibJS/Runtime/GlobalObject.h>
+#include <LibJS/Runtime/PromiseReaction.h>
+#include <LibJS/Runtime/PromiseResolvingElementFunctions.h>
+
+namespace JS {
+
+PromiseResolvingElementFunction::PromiseResolvingElementFunction(size_t index, PromiseValueList& values, PromiseCapability capability, RemainingElements& remaining_elements, Object& prototype)
+    : NativeFunction(prototype)
+    , m_index(index)
+    , m_values(values)
+    , m_capability(move(capability))
+    , m_remaining_elements(remaining_elements)
+{
+}
+
+void PromiseResolvingElementFunction::initialize(GlobalObject& global_object)
+{
+    Base::initialize(global_object);
+    define_direct_property(vm().names.length, Value(1), Attribute::Configurable);
+}
+
+Value PromiseResolvingElementFunction::call()
+{
+    if (m_already_called)
+        return js_undefined();
+    m_already_called = true;
+
+    return resolve_element();
+}
+
+void PromiseResolvingElementFunction::visit_edges(Cell::Visitor& visitor)
+{
+    Base::visit_edges(visitor);
+
+    visitor.visit(&m_values);
+    visitor.visit(m_capability.promise);
+    visitor.visit(m_capability.resolve);
+    visitor.visit(m_capability.reject);
+    visitor.visit(&m_remaining_elements);
+}
+
+PromiseAllResolveElementFunction* PromiseAllResolveElementFunction::create(GlobalObject& global_object, size_t index, PromiseValueList& values, PromiseCapability capability, RemainingElements& remaining_elements)
+{
+    return global_object.heap().allocate<PromiseAllResolveElementFunction>(global_object, index, values, capability, remaining_elements, *global_object.function_prototype());
+}
+
+PromiseAllResolveElementFunction::PromiseAllResolveElementFunction(size_t index, PromiseValueList& values, PromiseCapability capability, RemainingElements& remaining_elements, Object& prototype)
+    : PromiseResolvingElementFunction(index, values, move(capability), remaining_elements, prototype)
+{
+}
+
+Value PromiseAllResolveElementFunction::resolve_element()
+{
+    auto& vm = this->vm();
+    auto& global_object = this->global_object();
+
+    m_values.values[m_index] = vm.argument(0);
+
+    if (--m_remaining_elements.value == 0) {
+        auto values_array = Array::create_from(global_object, m_values.values);
+        return vm.call(*m_capability.resolve, js_undefined(), values_array);
+    }
+
+    return js_undefined();
+}
+
+}