feat: add support for Babel v8

[francescoparra]

Related to #535

Adapt ember-cli-babel to work with both @babel/core v7 and v8 by detecting the installed Babel major version at runtime and adjusting plugin options accordingly.

Changes for Babel 8 compatibility:

• @babel/plugin-proposal-decorators: use version: 'legacy' instead of legacy: true (removed in Babel 8)
• @babel/plugin-transform-runtime: omit useESModules option (removed in Babel 8, ESM is now auto-detected)
• @babel/plugin-transform-typescript: omit allowDeclareFields option (removed in Babel 8, always enabled)
• @babel/preset-env: strip loose and spec options (removed in Babel 8, use top-level assumptions instead)
• @babel/plugin-transform-class-static-block: omit legacy option (unknown options cause errors in Babel 8)
• @babel/plugin-transform-modules-amd: move moduleIds and getModuleId from root Babel options to plugin options (required by Babel 8)
• Update peerDependencies to accept @babel/core ^7.12.0 || ^8.0.0
• Widen all @babel/* dependency ranges to include ^8.0.0
• Add lib/babel-version.js utility for cached Babel version detection
• Add tests for all Babel 8 code paths

[francescoparra]

@mansona @NullVoxPopuli can someone have a look at this so we can merge it ASAP

[NullVoxPopuli]

@francescoparra,

ASAP

apologies, but a few things need to happen first

---

in your PR, all errors are:

not ok 1 Chrome 150.0 - [undefined ms] - 
  Global error: Uncaught Error: 
    Could not find module 
       `@babel/runtime/helpers/esm/toPropertyKey.js` 
        imported from `@babel/runtime/helpers/esm/defineProperty` 
        at http://localhost:7357/assets/vendor.js, line 266

However, ember-cli-babel also doesn't support those old environments very well (and we need to investigate),

This PR might require:

• feat: add support for Babel v8 #536

However, everything with babel is a bit of a mess, as bumping in-range versions causes the tests to fail

• Bump babel dependencies, use caret range for all (v7) #534
• (re)Demo of broccoli/AMD/loaderjs not supporting extensions #531

A fix here, but it looks like we all forgot about it

• Upgrade babel deps #530 (comment)

(and there are sure to be more, so PRs will need to be updated/rebased after the above is merged)

[francescoparra]

Thanks for the fast reply.

I agree that it probably makes sense to keep this PR focused on Babel 8 support and build on top of the fixes in #536/#534/#530 rather than duplicating them here.

I’ll keep an eye on those PRs and rebase/update this one as they land. If there’s a preferred order for these changes, let me know.

It would be great to ship this soon, hopefully it won't be too much of a challenge.