Support eslint 8.x

[Neirda24]

Hi!

I'm trying to use eslint >= 8 in order to have the private methods/properties syntax considered valid (using the babel configuration is such a pain to make it work...) Although it seems that the CLIEngine was removed and thus creating a bug when running encore.
See here for the post about CLIEngine: https://eslint.org/docs/8.0.0/user-guide/migrating-to-8.0.0#remove-cliengine
This is the error I get :

$ yarn watch
yarn run v1.22.15
$ encore dev --watch
Running webpack ...

  TypeError: eslint.CLIEngine is not a constructor

  - eslint.js:33 Object.getOptions
    [html]/[@symfony]/webpack-encore/lib/loaders/eslint.js:33:24

  - config-generator.js:408 ConfigGenerator.buildRulesConfig
    [html]/[@symfony]/webpack-encore/lib/config-generator.js:408:43

  - config-generator.js:79 ConfigGenerator.getWebpackConfig
    [html]/[@symfony]/webpack-encore/lib/config-generator.js:79:29

  - config-generator.js:626 module.exports
    [html]/[@symfony]/webpack-encore/lib/config-generator.js:626:22

  - index.js:1634 Encore.getWebpackConfig
    [html]/[@symfony]/webpack-encore/index.js:1634:16

  - EncoreProxy.js:51 Proxy.minDistance
    [html]/[@symfony]/webpack-encore/lib/EncoreProxy.js:51:53

  - webpack.config.js:31 Object.<anonymous>
    /var/www/html/webpack.config.js:31:25

  - loader:1101 Module._compile
    node:internal/modules/cjs/loader:1101:14

  - loader:1153 Object.Module._extensions..js
    node:internal/modules/cjs/loader:1153:10

  - loader:981 Module.load
    node:internal/modules/cjs/loader:981:32


error Command failed with exit code 1.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.

Maybe there is something I'm missing? Thanks for your replies.

[Kocal]

Hi, we need #985 to be merged for adding ESLint 8 support.

[Neirda24]

Nice thank you @Kocal and good work !