fix(eslint-plugin): [typedef] support "for..in", "for..of"

[octogonz]

Fixes #783

[typescript-eslint]

Thanks for the PR, @octogonz!

typescript-eslint is a 100% community driven project, and we are incredibly grateful that you are contributing to that community.

The core maintainers work on this in their personal time, so please understand that it may not be possible for them to review your work immediately.

Thanks again!

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[bradzacher]

LGTM - thanks for fixing this

[codecov]

Codecov Report

Merging #787 into master will decrease coverage by <.01%.
The diff coverage is 92.85%.

@@            Coverage Diff             @@
##           master     #787      +/-   ##
==========================================
- Coverage   94.21%   94.21%   -0.01%     
==========================================
  Files         112      112              
  Lines        4808     4821      +13     
  Branches     1334     1336       +2     
==========================================
+ Hits         4530     4542      +12     
  Misses        159      159              
- Partials      119      120       +1

Impacted Files	Coverage Δ
packages/eslint-plugin/src/rules/typedef.ts	95.91% <92.85%> (-1.31%)	⬇️