Pre-work to update to ESLint 8

[mattxwang]

Which issue, if any, is this issue related to?

Not an issue, but part of the discussion in #5645.

Is there anything in the PR that needs further explanation?

This PR slightly took on scope creep (from the initial ask to just update eslint-shared-config to major version 15. Here's my thought process:

1. First, I bumped the above
2. Then, this causes an error with eslint-plugin-jest. I could resolve this by manually reinstalling it as a dev dependency. I'm not sure if this is the right move; if it isn't, let me know and I can move this commit out of the PR.
3. Finally, I address the newly enabled jest/prefer-to-be rule, which was a simple find-and-replace.

Let me know if we'd prefer dependabot to handle. I'm using node 16 to generate the new package-lock, and we stay on lockfile v2.

[ybiquitous]

@mattxwang Thank you for creating this PR! 😄

I try removing eslint-plugin-jest, but it also works:

$ npm rm eslint-plugin-jest
...

$ npm ls eslint-plugin-jest
stylelint@14.0.1 /Users/koba/git/stylelint/stylelint
└─┬ eslint-config-stylelint@15.0.0
  └── eslint-plugin-jest@25.2.3

$ npm run lint:js -- --no-cache

> stylelint@14.0.1 lint:js
> eslint . --cache --max-warnings=0 "--no-cache"

[ntwb]

Then, this causes an error with eslint-plugin-jest. I could resolve this by manually reinstalling it as a dev dependency. I'm not sure if this is the right move; if it isn't, let me know and I can move this commit out of the PR.

Yeah, I had the same issue locally it worked without this, installing resolved it for me also /shrug

I try removing eslint-plugin-jest, but it also works:
@ybiquitous Depenadbot created another PR ~8 hours ago, same issue in that PR:

• Bump eslint from 7.32.0 to 8.2.0 #5702
• https://github.com/stylelint/stylelint/runs/4133769681?check_suite_focus=true

TypeError: Failed to load plugin 'jest' declared in 'package.json » eslint-config-stylelint': Class extends value undefined is not a constructor or null
Referenced from: /home/runner/work/stylelint/stylelint/node_modules/eslint-config-stylelint/index.js

[ntwb]

Per my comment #5699 (comment) I'm happy to approve this and land this as-is, we can revisit removing the eslint-plugin-jest plugin later

[ybiquitous]

@ntwb Ah, I see. Thanks for the feedback! 😄

LGTM 👍🏼

[mattxwang]

Thanks everyone! I can also try to see if removing eslint-plugin-jest resolves this in the future, maybe this is a node version thing and/or something resolved with ESLint 8?