refactor: updated eslint devDepencencies

[mfranzke]

Summary of changes:

It's important that someone else with ESLint, babel and webpack knowledge would have a look at these changes, especially my three code comments and the necessary evaluations.

• Updated all eslint and related dependencies to newer versions and
• extracted the eslintconfig within the live-server package to an external config file

added

• eslint-plugin-node:
  • Two of the previously introduced eslint rules have been moved to this plugin by ESLint v7.0.0:
    • no-mixed-requires -> node/no-mixed-requires
    • no-process-exit -> node/no-process-exit
• @babel/eslint-plugin

  Companion rules for @babel/eslint-parser. @babel/eslint-parser does a great job at adapting eslint for use with Babel, but it can't change the built-in rules to support experimental features. @babel/eslint-plugin re-implements problematic rules so they do not give false positives or negatives.

updated dependencies

• eslint
• eslint-plugin-import
• eslint-config-airbnb-base
• eslint-plugin-prettier
  • This breaking change drops support for old versions of ESLint, Prettier and Node. You must use at least ESLint v7.28.0, Prettier v2.0.0 and Node v12.0.0. Aside from that, usage of this plugin remains identical.
    We're matching the ESLint version with the updates from this pull request and Prettier even already, as well as Node.
• eslint-config-prettier

replaced

• "babel-eslint is now @babel/eslint-parser.", source https://www.npmjs.com/package/babel-eslint and https://babeljs.io/blog/2020/07/13/the-state-of-babel-eslint

Changed

rules

• Replaced deprecated and removed rules byESLint@7: https://eslint.org/docs/rules/#deprecated (see added section above as well)

extends

• https://github.com/prettier/eslint-plugin-prettier#recommended-configuration:

  This plugin ships with a plugin:prettier/recommended config that sets up both the plugin and eslint-config-prettier in one go.

  and read further on the section

  Exactly what does plugin:prettier/recommended do? Well, this is what it expands to:

ESLint and babel configs

sub-packages ESLint config file with an extend to root isn't necessary, as ESLint would search for that config anyhow, but we need to reference the root babel.config.js in our monorepo, compare to e.g.
https://babeljs.io/docs/en/config-files#root-babelconfigjson-file and https://babeljs.io/docs/en/config-files#file-relative-configuration

pending

• Why do we have both a .eslintrc.js and a .eslintrc.json in the root?

#updatingdependenciesbitbybitbybitbybitbybitbybitbybitbybit

[JosefBredereck]

I know this is an old PR which is still WIP, but could you elaborate why this gets removed when the PR only is about ESLint changes?

[JosefBredereck]

Same goes for the removal of this line