Moving to Node.js@16

[waldekmastykarz]

Following the Node.js release cadence, we're going to move to Node@16 as the main version used for development and testing. We'll keep testing Node@14 and Node@12 for backwards compatibility. We'll remove support for Node@12 on Apr 30, 2022, when it reaches end of life. More information https://nodejs.org/en/about/releases/.

[waldekmastykarz]

We've just merged the PR to upgrade the main Node.js version 16. From now on, when you're contributing to CLI for Microsoft, please use Node.js@16.