Drop support for old NodeJS versions

[pjonsson]

Sass 1.79 has started to output deprecation warnings and some of the warnings were fixed in #7273. This warning still remains:

DEPRECATION WARNING: The legacy JS API is deprecated and will be removed in Dart Sass 2.0.0.

and that would presumably be resolved by bumping sass-loader to v16, but that requires TerriaJS/TerriaMap to drop the support for the EOL'd Node 16.

The Node.js 16 LTS release had the last security support 11 September 2023 which is a little more than a year ago at the time of writing. The next LTS after 16 is 18, and the security support for Node.js 18 ends in just 7 months, 30 April 2025.

Without knowing any details about the security record of Node.js, my general experience with other software is that it's usually less work to run a supported version since taking care of security issues is someone else's problem, most of the time I'm set as long as I upgrade to the latest minor release. For updating to Sass 1.79 it's deprecation warnings rather than a security issue, but bumping sass-loader to v16 is probably the easiest fix to get rid of the warnings. Returning to security issues, TerriaJS/terriajs-server#169 is an example that would fix the security issues with the deprecated requests library by replacing it with a library that requires Node.js 20 (yes, other requests-like libraries exist, but switching to got seemed to be the easiest way forward when I looked into that).

What is the driver behind maintaining the support for Node.js 16, and when will that support be dropped?

Since Node.js 18 is comparatively near its end of life date already, I would personally like to see that support dropped as well since the decisions to drop Node.js versions seem to be fairly infrequent.