Add tests for #4786

[3flex]

Tests added to show that correctly formatted strings provided on the CLI are parsed as expected, and that the Gradle plugin maps the jvmTarget and languageVersion properties to those CLI flags as expected.

I've also improved the error message provided by the CLI when these flags cannot be parsed which should help narrow down issues.

[codecov]

Codecov Report

Merging #4801 (f4a2f27) into main (16bbc16) will increase coverage by 0.01%.
The diff coverage is 33.33%.

@@             Coverage Diff              @@
##               main    #4801      +/-   ##
============================================
+ Coverage     84.70%   84.72%   +0.01%     
  Complexity     3426     3426              
============================================
  Files           491      491              
  Lines         11253    11257       +4     
  Branches       2069     2069              
============================================
+ Hits           9532     9537       +5     
+ Misses          676      674       -2     
- Partials       1045     1046       +1     

Impacted Files	Coverage Δ
...gitlab/arturbosch/detekt/cli/ArgumentConverters.kt	73.33% <33.33%> (+4.10%)	⬆️
...ain/kotlin/io/gitlab/arturbosch/detekt/cli/Spec.kt	90.32% <0.00%> (+1.61%)	⬆️

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[BraisGabin]

Shouldn't we test the improved error messages?

[3flex]

We don't test the old ones :P

Feel free to do it in a new PR.