Upgrade to ESLint 8

[sindresorhus]

https://eslint.org/blog/2021/10/eslint-v8.0.0-released

Blocked by:

• Support ESLint v8 sindresorhus/eslint-plugin-unicorn#1488
• Support ESLint 8.x avajs/eslint-plugin-ava#335
• Support for ESLint v8 typescript-eslint/typescript-eslint#3738
• Support ESLint 8.x import-js/eslint-plugin-import#2211

[fregante]

Will you also change how dependencies are handled as part of this issue? That is, "don't depend on eslint-plugin-ava directly, but through eslint-config-xo"

[sindresorhus]

@fregante No, that's blocked by eslint/eslint#13481