Fix ExperimentalWarning about importAssertions

[danielfinke]

Use importAttributes instead of importAssertions if running on a Node.js version >= 18.20.0. On lower versions, continue to use importAssertions.

Left the comment re: removal of the deprecated option - can still remove Node.js 18 is no longer supported.

closes #7

[laverdet]

Thanks. This is a good continuation of the work from this commit 4b61a60 it looks like I missed some spots. I think a tweak to one of the expressions would make this more correct, let me know what you think.

[laverdet]

Good catch on the unused expression above.

I don't think this is what we want though. I believe this would prevent legacy asserts syntax from working after nodejs v18.20. v18 & v20 are supposed to be the transitional versions where either syntax works. So it gives teams a chance to migrate.

I think there need to be two distinct regular expressions. The first is the most aggressive/eager, in order to avoid deprecation warnings. That's the one you authored in loader.ts, it looks correct to me. The second one would be the least aggressive option, which should go here. I think it would be /^(?:16|17|18|19|20|21)/. So even if the user is using asserts syntax in nodejs v20 we will still allow it. It will hide the deprecation notice from them which is unfortunate but definitely not worth making our own deprecation notice.