[v13] Miniumum required node version updated to v20.10.0

[jesstelford]

Refs https://github.com/Shopify/polaris-internal/issues/1524

Node 16 is EOL, and Node 18 is in Maintenance Mode, so we're updating the minimum required Node version to v20.10.0 (the latest supported by node-releases/browserslist at the time this project started).

When is node used?

Node is used in 2 contexts:

1. By our consumers when they import, run, and bundle our libraries
2. By us, the Polaris team, while we develop our libraries

These are very different, and have their own configs within our repository...

1. Consumer's node version

When a consumer uses one of our libraries, they're importing whatever is in the build/* folder. Those assets are generated by our build process (Rollup) which transforms (via babel) whatever version of Javascript we write our code in into a version that's compatible with the targets setting we provide.

For example, Array#findLast was only made available in node v18, so when we write code like:

[1, 2, 3, 2, 1].findLast(x => x < 2);

The output will be different depending on our Babel config:

// with babel config: { targets: 'node 16.0' }
import "core-js/modules/esnext.array.find-last.js";
[1, 2, 3, 2, 1].findLast(x => x < 2);

// with babel config: { targets: 'node 18.0' }
[1, 2, 3, 2, 1].findLast(x => x < 2);

(try it here - set the "Env preset > Node" version to 18.0)

The node 18.0 example above does not include a polyfill for Array#findLast, which means if our consumers try to run Polaris in a node environment (eg; during SSR) that doesn't support Array#findLast, they will get an error.

The way we let our consumers know what is the minimum version of node they can use is via the packages.json#engines.node field. As long as this matches the version specified in Babel#targets, any consumer trying to install our library in an unsupported version of Node will receive an error.

This PR updates the minimum required node version of our consumers to 20.10.0.

2. Our node version while developing Polaris

Similarly, the tools we use to develop Polars (Babel, Postcss, etc) may have a minimum node version requirement.

They do it by specifying a package.json#engines.node version in their own library. Then when we install their package, if our version of node isn't compatible we'll receive an error.

However, the version of node required to run Babel has no impact on its ability to transform our code to work on older versions of node. As long as we tell Babel which version of node to output code for in targets, it doesn't matter what our .nvmrc file says.

#11739 updated the node version for developing with Polaris to 20.11.1.

[aaronccasanova]

Nice update!

[rtymchyk]

Why is this fixed to 20.10.0? Shouldn't it be >= 20.10.0? I am on 20.16.0 and this is causing build errors