LibJS: Fix .length attributes of various native functions

Namely the Proxy revocation, Promise resolving, Promise then/catch
finally, and Promise GetCapabilitiesExecutor functions.
They were all missing an explicit 'Attribute::Configurable' argument
and therefore incorrectly used the default attributes (writable,
enumerable, configurable).

Userland/Libraries/LibJS/Runtime/PromisePrototype.cpp

@@ -105,7 +105,7 @@ JS_DEFINE_NATIVE_FUNCTION(PromisePrototype::finally)
             });
             return promise->invoke(vm.names.then.as_string(), value_thunk);
         });
-        then_finally_function->define_property(vm.names.length, Value(1));
+        then_finally_function->define_property(vm.names.length, Value(1), Attribute::Configurable);
 
         // 27.2.5.3.2 Catch Finally Functions, https://tc39.es/ecma262/#sec-catchfinallyfunctions
         auto* catch_finally_function = NativeFunction::create(global_object, "", [constructor_handle = make_handle(constructor), on_finally_handle = make_handle(&on_finally.as_function())](auto& vm, auto& global_object) -> Value {
@@ -124,7 +124,7 @@ JS_DEFINE_NATIVE_FUNCTION(PromisePrototype::finally)
             });
             return promise->invoke(vm.names.then.as_string(), thrower);
         });
-        catch_finally_function->define_property(vm.names.length, Value(1));
+        catch_finally_function->define_property(vm.names.length, Value(1), Attribute::Configurable);
 
         then_finally = Value(then_finally_function);
         catch_finally = Value(catch_finally_function);

Userland/Libraries/LibJS/Runtime/PromiseReaction.cpp

@@ -25,6 +25,7 @@ PromiseCapability new_promise_capability(GlobalObject& global_object, Value cons
         Value reject { js_undefined() };
     } promise_capability_functions;
 
+    // 27.2.1.5.1 GetCapabilitiesExecutor Functions, https://tc39.es/ecma262/#sec-getcapabilitiesexecutor-functions
     auto* executor = NativeFunction::create(global_object, "", [&promise_capability_functions](auto& vm, auto& global_object) -> Value {
         auto resolve = vm.argument(0);
         auto reject = vm.argument(1);
@@ -41,7 +42,7 @@ PromiseCapability new_promise_capability(GlobalObject& global_object, Value cons
         promise_capability_functions.reject = reject;
         return js_undefined();
     });
-    executor->define_property(vm.names.length, Value(2));
+    executor->define_property(vm.names.length, Value(2), Attribute::Configurable);
 
     MarkedValueList arguments(vm.heap());
     arguments.append(executor);

Userland/Libraries/LibJS/Runtime/PromiseResolvingFunction.cpp

@@ -27,7 +27,7 @@ PromiseResolvingFunction::PromiseResolvingFunction(Promise& promise, AlreadyReso
 void PromiseResolvingFunction::initialize(GlobalObject& global_object)
 {
     Base::initialize(global_object);
-    define_property(vm().names.length, Value(1));
+    define_property(vm().names.length, Value(1), Attribute::Configurable);
 }
 
 Value PromiseResolvingFunction::call()

Userland/Libraries/LibJS/Runtime/ProxyConstructor.cpp

@@ -79,7 +79,7 @@ JS_DEFINE_NATIVE_FUNCTION(ProxyConstructor::revocable)
         proxy.revoke();
         return js_undefined();
     });
-    revoker->define_property(vm.names.length, Value(0));
+    revoker->define_property(vm.names.length, Value(0), Attribute::Configurable);
 
     auto* result = Object::create(global_object, global_object.object_prototype());
     result->define_property(vm.names.proxy, proxy);