Can not enable `syntax-class-properties` with other fields related plugins

Bug Report

• I would like to work on a fix!

Current behavior

• REPL

Input Code

export class Foo {
  #bar = 'bar'
}

Expected behavior

I’d like to keep class properties as-is.

Babel Configuration (babel.config.js, .babelrc, package.json#babel, cli command, .eslintrc)

• Filename: babel.config.js

module.exports = {
  plugins: [
    '@babel/syntax-class-properties',
    '@babel/proposal-private-methods',
  ],
}

Environment

- Babel version(s): v7.12.10
- Node/npm version: Node v12.20.0/npm 6.14.9
- OS: macOS 11.2 Beta
- Monorepo: no
- How you are using Babel: API directly

Possible Solution

Check syntax-class-properties instead of proposal-class-properties for class fields

Additional context

[nicolo-ribaudo]

This is probably fixed by part of https://github.com/babel/babel/pull/12250, I can split that PR in two separate PRs.

[nicolo-ribaudo]

I’m preparing https://github.com/babel/babel/pull/13260 as an alternative for #12250, which gives better and easier control on how the different class features transforms interact.