LibJS: Change ExecutionContext's arguments list to a MarkedValueList

The test262 tests under RegExp/property-escapes/generated will invoke
Reflect.apply with up to 10,000 arguments at a time. In LibJS, when the
call stack reached VM::call_internal, we transfer those arguments from
a MarkedValueList to the execution context's arguments Vector.

Because these types differ (MarkedValueList is a Vector<Value, 32>), the
arguments are copied rather than moved. By changing the arguments vector
to a MarkedValueList, we can properly move the passed arguments over.

This shaves about 2 seconds off the following test262 test (from 15sec):
  RegExp/property-escapes/generated/General_Category_-_Decimal_Number.js

Userland/Libraries/LibJS/Runtime/VM.h

@@ -43,11 +43,16 @@ struct ScopeFrame {
 };
 
 struct ExecutionContext {
+    explicit ExecutionContext(Heap& heap)
+        : arguments(heap)
+    {
+    }
+
     const ASTNode* current_node { nullptr };
     FlyString function_name;
     FunctionObject* function { nullptr };
     Value this_value;
-    Vector<Value> arguments;
+    MarkedValueList arguments;
     Object* arguments_object { nullptr };
     Environment* lexical_environment { nullptr };
     Environment* variable_environment { nullptr };