Remove deprecated KotlinExtension

[3flex]

This was deprecated in detekt 1.3.0 - it's time to say goodbye.

[codecov]

Codecov Report

Merging #4063 (061d84e) into main (026066f) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##               main    #4063   +/-   ##
=========================================
  Coverage     83.58%   83.58%           
  Complexity     3186     3186           
=========================================
  Files           459      459           
  Lines          9099     9099           
  Branches       1772     1772           
=========================================
  Hits           7605     7605           
  Misses          561      561           
  Partials        933      933           

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[cortinico]

it's time to say goodbye.

Agree.
As a side note: I'm even unsure of how users would use this API in their gradle file. Was it something like?

this.detekt {
    ...
}

Asking as we probably want to add something to the release notes about it

[3flex]

Was it something like?

It was just:

detekt {

}

The problem is the plugin wasn't being applied correctly by some users, so the type-safe accessors generated for the Kotlin DSL weren't being generated. This is a configuration problem, not something to do with the plugin, but this helper provided a workaround.

The helper isn't necessary if the plugin is applied properly. Users should be familiar with Gradle's Kotlin DSL primer. I'm not sure if we need something in the release notes since the deprecation message has had a link to this document since 2019.