v2 addon conversion?

[NullVoxPopuli]

Idk how much detail you want in this issue, but when I heard of the babel transform changes in the 2.3.2 version, I was expecting to have to modify my babel config. I later found that this happens automatically for me in the index.js -- which can certainly be a nice ability for people don't want to think about babel.

For some background, here is the process:

• https://github.com/embroider-build/embroider/blob/main/PORTING-ADDONS-TO-V2.md

Here are some example "mega" PRs were v2 conversions happened (these all also switch to pnpm, so that's why the diff is massive):

• Covert to V2 addon (a real npm package!) emberjs/ember-string#345 -- this one explains the process in a step-by-step way in the last comment
• Convert to V2 Addon NullVoxPopuli/ember-resources#263
• feat: convert to v2 format NullVoxPopuli/ember-popperjs#142

But anywho -- a goal I have for ember + babel is to be able to pick and choose babel plugins for optimal output -- right now there is a bug in @babel/plugin-proposal-decorators that requires the class-properties plugin, and I'd like to omit class-properties plugins from all my apps (because browsers natively support them) -- and providing a way for consumers of ember-concurrency to opt in/out of the babel plugin would be a good step in that direction as well. :D

[machty]

Done #551