fix(eslint-plugin): [array-type] fix issues with readonly option

[sonallux]

Fix #2323

[typescript-eslint]

Thanks for the PR, @jsone-studios!

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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[codecov]

Codecov Report

Merging #2667 into master will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2667      +/-   ##
==========================================
+ Coverage   92.78%   92.81%   +0.02%     
==========================================
  Files         294      294              
  Lines        9676     9644      -32     
  Branches     2713     2701      -12     
==========================================
- Hits         8978     8951      -27     
+ Misses        330      328       -2     
+ Partials      368      365       -3     

Flag	Coverage Δ
#unittest	92.81% <100.00%> (+0.02%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
packages/eslint-plugin/src/rules/array-type.ts	98.63% <100.00%> (+4.34%)	⬆️

[bradzacher]

LGTM - thanks heaps for all of your work here, esp for the comprehensive test coverage!