Reduce visibility

[BraisGabin]

We don't need to expose the implementations outside the file. And we don't want to mix builders and actual implementations so we should not make the builders implement the interfaces.

[codecov]

Codecov Report

Merging #3326 (37406b7) into master (6b065a8) will decrease coverage by 0.02%.
The diff coverage is 94.87%.

@@             Coverage Diff              @@
##             master    #3326      +/-   ##
============================================
- Coverage     80.28%   80.25%   -0.03%     
+ Complexity     2714     2713       -1     
============================================
  Files           445      445              
  Lines          8196     8196              
  Branches       1558     1558              
============================================
- Hits           6580     6578       -2     
- Misses          778      780       +2     
  Partials        838      838              

Impacted Files	Coverage Δ	Complexity Δ
...github/detekt/tooling/dsl/ExtensionsSpecBuilder.kt	94.44% <80.00%> (-5.56%)	10.00 <2.00> (-1.00)
...io/github/detekt/tooling/dsl/ProjectSpecBuilder.kt	90.90% <83.33%> (-9.10%)	5.00 <4.00> (ø)
...o/github/detekt/tooling/dsl/BaselineSpecBuilder.kt	100.00% <100.00%> (ø)	4.00 <3.00> (ø)
...o/github/detekt/tooling/dsl/CompilerSpecBuilder.kt	100.00% <100.00%> (ø)	5.00 <4.00> (ø)
.../io/github/detekt/tooling/dsl/ConfigSpecBuilder.kt	89.47% <100.00%> (ø)	7.00 <6.00> (ø)
.../github/detekt/tooling/dsl/ExecutionSpecBuilder.kt	100.00% <100.00%> (ø)	5.00 <4.00> (ø)
...io/github/detekt/tooling/dsl/LoggingSpecBuilder.kt	100.00% <100.00%> (ø)	5.00 <0.00> (ø)
...github/detekt/tooling/dsl/ProcessingSpecBuilder.kt	100.00% <100.00%> (ø)	11.00 <0.00> (ø)
...io/github/detekt/tooling/dsl/ReportsSpecBuilder.kt	100.00% <100.00%> (ø)	3.00 <1.00> (ø)
...n/io/github/detekt/tooling/dsl/RulesSpecBuilder.kt	94.73% <100.00%> (ø)	7.00 <0.00> (ø)

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