eslint: switch from custom rules to eslint-config-wikimedia

[NovemLinguae]

https://github.com/wikimedia/eslint-config-wikimedia

Why switch?

• it's standard for wikimedia projects
• it has some cool features such as jquery deprecation warnings, and enforcing a specific version of JavaScript
• I believe it has many more rules than our previous configuration, which will help with identifying areas of the code to modernize

What this patch does

• delete all old linter rules, except for these rules I carried over:
  • no-nested-ternary
  • no-restricted-syntax for .done() and .fail()
• add eslint-config-wikimedia and its default rules
• disable controversial rules such as
  • whitespace in parentheses (space-in-parens, space-before-function-paren, array-bracket-spacing, computed-property-spacing, object-curly-spacing)
  • max line length 100 (max-len)
• disable some other rules
  • indent because it would involve touching every line, messing up git blame
  • couple others
• set it to ES6 since wikimedia grade A support is now on ES6
• warn/error for syntax or internal functions higher than ES6 (more thoroughly than the old >ES6 detection we were using)
• apply all autofixes
  • converting var to let/const (no-var)
  • wrap-iife
  • no-multiple-empty-lines
  • no-multi-spaces
  • quote-props
  • unicorn/prefer-string-slice
  • no-unneeded-ternary
  • dot-location
  • jsdoc/require-asterisk-prefix
  • couple others
• set all remaining detected violations to "warn" for now, until they can be fixed in future patches

All changes in this patch are related to installing and configuring eslint-config-wikimedia, or applying autofixes. No manual changes in this patch.

[NovemLinguae]

I've decided I don't like the substring() -> slice(Math.max) conversion. Too verbose. Note to self: rollback those 9 auto fixes, and set unicorn/prefer-string-slice to off

[NovemLinguae]

Note to self: I could do the "indent" autofix and add that commit to a .git-blame-ignore-revs file, to avoid spamming git blame.

https://docs.github.com/en/repositories/working-with-files/using-files/viewing-a-file#ignore-commits-in-the-blame-view

[NovemLinguae]

This patch is too big. I'm going to close and resubmit it in favor of a smaller patch, so I can do this more incrementally.