[core] Allow for..of loops

[michaldudak]

Removed the eslint-config-airbnb-base package. It is meant to be used in non-React apps.
The primary reason for its removal is to allow using iterators and the for..of loops, as the browser support is good (the spec is a part of ES2015).

Removal of this package also removes 3 additional no-restricted-syntax rules:

{
  selector: 'ForInStatement',
  message: 'for..in loops iterate over the entire prototype chain, which is virtually never what you want. Use Object.{keys,values,entries}, and iterate over the resulting array.',
},
{
  selector: 'LabeledStatement',
  message: 'Labels are a form of GOTO; using them makes code confusing and hard to maintain and understand.',
},
{
  selector: 'WithStatement',
  message: '`with` is disallowed in strict mode because it makes code impossible to predict and optimize.',
},

However, we have other rules that prevent writing unsafe code using these constructs: guard-for-in, no-labels, and no-with.

Note that writing for..of loops in projects in this repo is still prevented by tsconfig's target being set to "ES5". Changing this should be discussed first in a separate PR.

[mui-bot]

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[Janpot]

Not necessarily part of this PR, but is this in intentional? Is it required to traverse prototype properties here?

Another thing I noticed while sniffing around this code is that we can likely easily optimize occurences of str.indexOf(search) === 0 to the more performant string.startsWith(search)

[michaldudak]

Considering https://github.com/mui/material-ui/pull/13919/files#r241988655, this code may benefit from a more thorough review (cc @DiegoAndai) ;)
I'd like to keep this PR focused on eslint changes only, though.

[DiegoAndai]

@Janpot may I ask you to create an issue for the optimization? that way we can ask the community for contributions.

[Janpot]

I'll verify first whether it's a real optimization

[Janpot]

Just a small comment with possible side-quests 🙂