Sync with latest addon blueprint and use decorator-transforms

[SergeAstapov]

v2 addon blueprint: https://github.com/embroider-build/addon-blueprint

Minor gain: using decorator-transforms reduced bundle size for the app.

[SergeAstapov]

side note: funnily enough, v5 scenarios pass only because repo uses yarn and yarn incorrectly handles peer dependencies

[villander]

Couple requested changes!

@SergeAstapov could you please describe what's size do you mean about the app? Are you talking about the testing-app?

[SergeAstapov]

Couple requested changes!

@SergeAstapov could you please describe what's size do you mean about the app? Are you talking about the testing-app?

added link to PR description.

RE: decorator-transforms/
You may read about this package in https://github.com/ef4/decorator-transforms/
now it comes from v2 addon blueprint, see https://github.com/embroider-build/addon-blueprint/blob/main/files/__addonLocation__/package.json#L37

TL;DR @babel/plugin-proposal-decorators has large footprint in terms of compiled code size. In our app we saw 18% reduction in size for vendor.js and app.js once we introduced decorator-transforms/ and disabled @babel/plugin-proposal-decorators.

[villander]

We can merge this PR when CI get green again

[SergeAstapov]

@villander this is refreshed with the latest blueprint as of now and CI is passing