Remove direct options to @babel/plugin-class-features

[nicolo-ribaudo]

Q	A
Fixed Issues?
Patch: Bug Fix?
Major: Breaking Change?	⚠️ We should merge this before the next release
Minor: New Feature?
Tests Added + Pass?
Documentation PR Link
Any Dependency Changes?
License	MIT

This PR removes the ability of using the class-features plugin like this:

{
  "plugins": [
    ["@babel/plugin-class-features", { "decorators": true }]
  ]
}

Since it could cause problems because it behaves differently from how other plugins behave (see #8130 (comment)).
With this PR only the old packages (@babel/plugin-proposal-class-properties, etc) can be used to configure @babel/plugin-class-features.

[babel-bot]

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/9417/

[Andarist]

What's going to happen when somebody is going to use this plugin directly? As in:

{
  "plugins": [
    "@babel/plugin-class-features"
  ]
}

[nicolo-ribaudo]

It is a noop. I could throw if you prefer, but I don't think that it is needed.

[Andarist]

IMHO would be good to throw or at least warn the user - somebody mind find this plugin and try to use it manually and be surprised that it's not working.

[andrewmiller1]

It's pretty straightforward to declare what class features you want using plugin-class-features. Why not make this the new way of doing it? I just spent an hour trying to figure out how to do it the "old way" and now I have to give up. Can't see what options could even map to this using what existed before (it had been confusing before anyway). Just a random user's two cents

[nicolo-ribaudo]

Before that @babel/plugin-class-features you had a configuration similar to this:

{
  plugins: [
    "@babel/plugin-proposal-private-properties",
    "@babel/plugin-proposal-decorators"
  ]
}

Now you should have the same identical config:

{
  plugins: [
    "@babel/plugin-proposal-private-properties",
    "@babel/plugin-proposal-decorators"
  ]
}

The two plugins internally use @babel/plugin-class-features, but you shouldn't care since it is an implementation detail.

[nicolo-ribaudo]

@babel/babel If it won't be possible to use this plugin directly, I think that its exisence only creates confusion. WDYT about renaming it to @babel/helper-transform-class-features?

[nicolo-ribaudo]

Closing, #9083 is better