Import Attributes support in Acorn

[thescientist13]

Summary

Playing the long game a bit, but as Import Attributes are only currently Stage 3, it is not supported in some key dependencies yet, like acorn. (made a little repro repo to confirm)

However, it is supported in NodeJS and browsers as was implemented in #923 and ProjectEvergreen/wcc#157.

Will also want to track this along with an upgrade to latest Rollup, which actually took out the ability to pass in custom Acorn plugins - #1087 (comment)

Details

As part of those PRs for Greenwood and WCC, a community plugin was used to bridge the gap, however when the spec graduates to Stage 4 and / or acorn adopts it, we can / should (for both WCC and Greenwood):

1. Upgrade acorn version
2. Will probably need to rollback custom parser changes
3. Remove the dependency on acorn-import-attributes