Move gradle testkit test back to test/

[chao2zhang]

Problem

IntelliJ IDE by default will not recognize our custom source set as test. Therefore the dependencies can be inferred incorrectly. See the screenshot:

It still won't work even if we use the idea gradle plugin as described in IDEA-151925.

Another problem with respect to IDE integration is that the code generated DEFAULT_DETEKT_VERSION cannot be correctly displayed.

Main change

Moving these testkit tests back to test/ would significantly improve the IDE experience: there is no IDE warnings or errors and we can continue run tests in IntelliJ.

Other changes

• In addition, uses processResources to replace the code generation to pass build time values to runtime.
• Removes an unnecessary println.

[codecov]

Codecov Report

Merging #3504 (119443a) into master (da6c969) will increase coverage by 0.06%.
The diff coverage is 75.00%.

@@             Coverage Diff              @@
##             master    #3504      +/-   ##
============================================
+ Coverage     77.56%   77.62%   +0.06%     
- Complexity     2804     2806       +2     
============================================
  Files           461      461              
  Lines          8668     8671       +3     
  Branches       1676     1676              
============================================
+ Hits           6723     6731       +8     
+ Misses         1040     1035       -5     
  Partials        905      905              

Impacted Files	Coverage Δ	Complexity Δ
...kotlin/io/gitlab/arturbosch/detekt/DetektPlugin.kt	6.25% <75.00%> (+6.25%)	0.00 <0.00> (ø)
...b/arturbosch/detekt/extensions/DetektReportType.kt	83.33% <0.00%> (+83.33%)	2.00% <0.00%> (+2.00%)

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