feat(eslint-plugin): add prefer-readonly-parameters

[bradzacher]

Fixes #514

cc @sindresorhus

[typescript-eslint]

Thanks for the PR, @bradzacher!

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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[sindresorhus]

I haven't reviewed the code itself, but the docs look good.

[codecov]

Codecov Report

Merging #1513 into master will increase coverage by 0.03%.
The diff coverage is 96.98%.

@@            Coverage Diff            @@
##           master   #1513      +/-   ##
=========================================
+ Coverage   95.56%   95.6%   +0.03%     
=========================================
  Files         144     145       +1     
  Lines        6701    6755      +54     
  Branches     1922    1936      +14     
=========================================
+ Hits         6404    6458      +54     
  Misses        107     107              
  Partials      190     190

Impacted Files	Coverage Δ
packages/eslint-plugin/src/rules/ban-types.ts	100% <100%> (ø)	⬆️
...es/eslint-plugin/src/rules/no-floating-promises.ts	100% <100%> (ø)	⬆️
...kages/eslint-plugin/src/rules/no-base-to-string.ts	100% <100%> (ø)
...plugin/src/rules/explicit-module-boundary-types.ts	86.2% <100%> (ø)	⬆️
...-plugin/src/rules/explicit-member-accessibility.ts	97.1% <100%> (+0.73%)	⬆️
packages/eslint-plugin/src/rules/typedef.ts	97.05% <100%> (ø)	⬆️
...ages/eslint-plugin/src/rules/default-param-last.ts	100% <100%> (ø)	⬆️
packages/eslint-plugin/src/util/astUtils.ts	80.55% <50%> (ø)	⬆️
packages/eslint-plugin/src/rules/return-await.ts	95.71% <95.45%> (ø)	⬆️
...int-plugin/src/rules/strict-boolean-expressions.ts	96.77% <96.42%> (ø)	⬆️
... and 9 more