src/common/ast-path.js/AstPath/each
class AstPath:  each(callback, ...names) {
    const { stack } = this;
    const { length } = stack;
    let value = getLast(stack);

    for (const name of names) {
      value = value[name];
      stack.push(name, value);
    }

    for (let i = 0; i < value.length; ++i) {
      stack.push(i, value[i]);
      callback(this, i, value);
      stack.length -= 2;
    }

    stack.length = length;
  }