convert to ESM so we can use yeoman-generator@v7 and greater

[shazron]

We are already dynamically importing yeoman-test via #241 .
This will be a major version upgrade.

Any users of this lib (which will be made into an ESM) must:

• not use any explicit paths from the main export (unless we explicitly provide this path)
• dynamically import this lib, if used from commonjs

[aiojbot]

JIRA issue created: https://jira.corp.adobe.com/browse/ACNA-2759