remove support for Node.js 14 and 16

[davidjgoss]

Currently we support Node.js 14 and 16. Per their release schedule, 14 has already been EOL'd, and 16 will follow on 11 Sep 2023 - in just a few days time as I write this.

For our next major release (10.0.0), we should drop both 14 and 16.

Once this is done, we'll be able to explore adopting some newer features, including node: import specifiers and even WHATWG streams. We could also reduce some dependencies by using new JavaScript and Node.js utils like structuredClone and tmpdir.

Also, we can go upstream and apply this to the various @cucumber/* libraries like gherkin etc.

(A note for future, we ought to be more prompt about following suit when Node.js EOL's a release, as it always brings benefits and helps move the ecosystem along.)