[ddc] Incorrect defaulting of named arguments with certain names

[rakudrama]

The property lookup in the JavaScript object 'bag' of named arguments finds methods from Object.prototype.
For example

foo({valueOf = 1}) => print(valueOf);

main() {
  foo(2); // Prints `2`
  foo();  // Prints a JavaScript function, not `1`.
}

See test https://dart-review.googlesource.com/c/sdk/+/377360