LibJS: Move initialize_instance_elements() from VM to Object

This makes more sense as an Object method rather than living within the
VM class for no good reason. Most of the other 7.3.xx AOs already work
the same way.
Also add spec comments while we're here.

Userland/Libraries/LibJS/AST.cpp

@@ -524,7 +524,7 @@ Completion SuperCall::execute(Interpreter& interpreter) const
     [[maybe_unused]] auto& f = this_er.function_object();
 
     // 11. Perform ? InitializeInstanceElements(result, F).
-    TRY(vm.initialize_instance_elements(*result, f));
+    TRY(result->initialize_instance_elements(f));
 
     // 12. Return result.
     return Value { result };

Userland/Libraries/LibJS/Bytecode/Op.cpp

@@ -678,7 +678,7 @@ ThrowCompletionOr<void> SuperCall::execute_impl(Bytecode::Interpreter& interpret
     // NOTE: This is implied by the strong C++ type.
 
     // 11. Perform ? InitializeInstanceElements(result, F).
-    TRY(vm.initialize_instance_elements(*result, f));
+    TRY(result->initialize_instance_elements(f));
 
     // 12. Return result.
     interpreter.accumulator() = result;

Userland/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.cpp

@@ -231,7 +231,7 @@ ThrowCompletionOr<Object*> ECMAScriptFunctionObject::internal_construct(MarkedVe
         ordinary_call_bind_this(callee_context, this_argument);
 
         // b. Let initializeResult be Completion(InitializeInstanceElements(thisArgument, F)).
-        auto initialize_result = vm.initialize_instance_elements(*this_argument, *this);
+        auto initialize_result = this_argument->initialize_instance_elements(*this);
 
         // c. If initializeResult is an abrupt completion, then
         if (initialize_result.is_throw_completion()) {

Userland/Libraries/LibJS/Runtime/Object.cpp

@@ -606,6 +606,27 @@ ThrowCompletionOr<void> Object::define_field(ClassFieldDefinition const& field)
     return {};
 }
 
+// 7.3.33 InitializeInstanceElements ( O, constructor ), https://tc39.es/ecma262/#sec-initializeinstanceelements
+ThrowCompletionOr<void> Object::initialize_instance_elements(ECMAScriptFunctionObject& constructor)
+{
+    // 1. Let methods be the value of constructor.[[PrivateMethods]].
+    // 2. For each PrivateElement method of methods, do
+    for (auto const& method : constructor.private_methods()) {
+        // a. Perform ? PrivateMethodOrAccessorAdd(O, method).
+        TRY(private_method_or_accessor_add(method));
+    }
+
+    // 3. Let fields be the value of constructor.[[Fields]].
+    // 4. For each element fieldRecord of fields, do
+    for (auto const& field : constructor.fields()) {
+        // a. Perform ? DefineField(O, fieldRecord).
+        TRY(define_field(field));
+    }
+
+    // 5. Return unused.
+    return {};
+}
+
 // 10.1 Ordinary Object Internal Methods and Internal Slots, https://tc39.es/ecma262/#sec-ordinary-object-internal-methods-and-internal-slots
 
 // 10.1.1 [[GetPrototypeOf]] ( ), https://tc39.es/ecma262/#sec-ordinary-object-internal-methods-and-internal-slots-getprototypeof

Userland/Libraries/LibJS/Runtime/Object.h

@@ -108,6 +108,7 @@ public:
     ThrowCompletionOr<Value> private_get(PrivateName const& name);
     ThrowCompletionOr<void> private_set(PrivateName const& name, Value value);
     ThrowCompletionOr<void> define_field(ClassFieldDefinition const&);
+    ThrowCompletionOr<void> initialize_instance_elements(ECMAScriptFunctionObject& constructor);
 
     // 10.1 Ordinary Object Internal Methods and Internal Slots, https://tc39.es/ecma262/#sec-ordinary-object-internal-methods-and-internal-slots
 

Userland/Libraries/LibJS/Runtime/VM.cpp

@@ -608,17 +608,6 @@ ThrowCompletionOr<Reference> VM::resolve_binding(FlyString const& name, Environm
     //       But this is not actually correct as GetIdentifierReference (or really the methods it calls) can throw.
 }
 
-// 7.3.33 InitializeInstanceElements ( O, constructor ), https://tc39.es/ecma262/#sec-initializeinstanceelements
-ThrowCompletionOr<void> VM::initialize_instance_elements(Object& object, ECMAScriptFunctionObject& constructor)
-{
-    for (auto& method : constructor.private_methods())
-        TRY(object.private_method_or_accessor_add(method));
-
-    for (auto& field : constructor.fields())
-        TRY(object.define_field(field));
-    return {};
-}
-
 // 9.4.4 ResolveThisBinding ( ), https://tc39.es/ecma262/#sec-resolvethisbinding
 ThrowCompletionOr<Value> VM::resolve_this_binding()
 {

Userland/Libraries/LibJS/Runtime/VM.h

@@ -206,8 +206,6 @@ public:
     Function<void(Promise&)> on_promise_unhandled_rejection;
     Function<void(Promise&)> on_promise_rejection_handled;
 
-    ThrowCompletionOr<void> initialize_instance_elements(Object& object, ECMAScriptFunctionObject& constructor);
-
     CustomData* custom_data() { return m_custom_data; }
 
     ThrowCompletionOr<void> destructuring_assignment_evaluation(NonnullRefPtr<BindingPattern> const& target, Value value);