fix(eslint-plugin): [no-implied-eval] correct logic for ts3.8

[bradzacher]

Fixes #1642

Tested this against 3.7.5 and 3.8.2 and it works in both.

The changes in the tests were just whitespace changes and changing { code: `...` } to be inline.

[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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[codecov]

Codecov Report

Merging #1652 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1652      +/-   ##
==========================================
+ Coverage   95.53%   95.54%   +0.01%     
==========================================
  Files         142      142              
  Lines        6623     6627       +4     
  Branches     1896     1897       +1     
==========================================
+ Hits         6327     6332       +5     
  Misses        106      106              
+ Partials      190      189       -1

Impacted Files	Coverage Δ
...ackages/eslint-plugin/src/rules/no-implied-eval.ts	97.82% <100%> (+1.9%)	⬆️
packages/eslint-plugin/src/rules/ban-types.ts	100% <0%> (ø)	⬆️
...ages/eslint-plugin/src/rules/default-param-last.ts	100% <0%> (ø)	⬆️