feat(linter): Implement no-undef-init

[radu2147]

Related to #479

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[codspeed-hq]

CodSpeed Performance Report

Merging #6267 will not alter performance

_{Comparing radu2147:feat/no-undef-init (44045f3) with main (e0a3378)}

Summary

✅ 29 untouched benchmarks

[DonIsaac]

I have a feeling that we have a rule doing this already, but I'm not certain. @camc314 are you aware of this?

[radu2147]

There are no-undefined and no-undef rules as well but those are different from this one. Looked it up by the eslint name and didn't find any files that matched it

[camc314]

duplicate of no-useless-undefined ?

  × eslint(no-undefined): Disallow the use of `undefined` as an identifier
   ╭─[./test.js:1:9]
 1 │ let l = undefined;
   ·         ─────────
   ╰────
  help: Unexpected use of undefined.

  × eslint(no-unused-vars): Variable 'l' is declared but never used.
   ╭─[./test.js:1:5]
 1 │ let l = undefined;
   ·     ┬
   ·     ╰── 'l' is declared here
   ╰────
  help: Consider removing this declaration.

  × eslint-plugin-unicorn(no-useless-undefined): Do not use useless `undefined`.
   ╭─[./test.js:1:9]
 1 │ let l = undefined;
   ·         ─────────
   ╰────
  help: Consider removing `undefined` or using `null` instead.

Finished in 19ms on 1 file with 

[radu2147]

Yes, it seems that no-useless-undefined treats a more general case which involves this one as well. @camc314 should we mark the no-undef-init rule in linter product plan for eslint as done, in this case?

Also I noticed that no-lonely-if is also done in unicorn