Refactor gradle integration test

[chao2zhang]

This is mostly meant to reorganize the integration tests as I am adding integration tests for Detekt Android.

• Changed detektConfig in Submodule to buildFileContent as I am going to apply different android build logic for each submodule.
• Remove ProjectLayout as a data class and it feels inefficient to create a new ProjectLayout each time when calling withSubmodule

[codecov]

Codecov Report

Merging #3487 (237264b) into master (fab88df) will decrease coverage by 0.21%.
The diff coverage is 71.49%.

@@             Coverage Diff              @@
##             master    #3487      +/-   ##
============================================
- Coverage     80.28%   80.06%   -0.22%     
- Complexity     2785     2864      +79     
============================================
  Files           454      458       +4     
  Lines          8415     8584     +169     
  Branches       1609     1663      +54     
============================================
+ Hits           6756     6873     +117     
- Misses          787      794       +7     
- Partials        872      917      +45     

Impacted Files	Coverage Δ	Complexity Δ
...ab/arturbosch/detekt/cli/DetektProgressListener.kt	83.33% <ø> (ø)	4.00 <0.00> (ø)
...io/gitlab/arturbosch/detekt/core/KtFileModifier.kt	0.00% <ø> (ø)	0.00 <0.00> (ø)
.../arturbosch/detekt/core/baseline/BaselineFacade.kt	77.77% <0.00%> (ø)	6.00 <2.00> (ø)
...hub/detekt/metrics/processors/AbstractProcessor.kt	83.33% <ø> (ø)	3.00 <0.00> (ø)
...trics/processors/AbstractProjectMetricProcessor.kt	83.33% <ø> (ø)	3.00 <0.00> (ø)
...detekt/metrics/processors/PackageCountProcessor.kt	91.66% <ø> (ø)	3.00 <0.00> (ø)
...ain/kotlin/io/github/detekt/metrics/LinesOfCode.kt	87.50% <50.00%> (-5.61%)	0.00 <0.00> (ø)
.../arturbosch/detekt/rules/style/UseIsNullOrEmpty.kt	58.66% <58.66%> (ø)	40.00 <40.00> (?)
...urbosch/detekt/rules/bugs/UnreachableCatchBlock.kt	72.22% <72.22%> (ø)	9.00 <9.00> (?)
...gitlab/arturbosch/detekt/rules/style/UseOrEmpty.kt	76.08% <76.08%> (ø)	13.00 <13.00> (?)
... and 13 more

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