Adopt ES2020 features

[minggangw]

Currently, rclnodejs supports node LTS versions (14, 16 and 18 as day of 3/6/2023), we can leverage more features introduced since ES2020, for example:

• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Optional_chaining
• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Nullish_coalescing