Add a test for UndocumentedPublicClass and fun interfaces

[cortinico]

Adding a test case to validate UndocumentedPublicClass against fun interfaces.

See #3372 for reference.

[codecov]

Codecov Report

Merging #3374 (1af0769) into master (f39eb76) will increase coverage by 0.00%.
The diff coverage is 78.57%.

@@            Coverage Diff            @@
##             master    #3374   +/-   ##
=========================================
  Coverage     80.30%   80.31%           
  Complexity     2721     2721           
=========================================
  Files           445      445           
  Lines          8241     8248    +7     
  Branches       1564     1566    +2     
=========================================
+ Hits           6618     6624    +6     
  Misses          785      785           
- Partials        838      839    +1     

Impacted Files	Coverage Δ	Complexity Δ
...tlab/arturbosch/detekt/core/reporting/Reporting.kt	94.11% <ø> (ø)	0.00 <0.00> (ø)
.../main/kotlin/io/github/detekt/parser/KtCompiler.kt	77.27% <0.00%> (-4.55%)	8.00 <0.00> (ø)
...etekt/core/tooling/ProcessingSpecSettingsBridge.kt	92.85% <50.00%> (-7.15%)	0.00 <0.00> (ø)
...io/github/detekt/report/sarif/SarifOutputReport.kt	94.73% <90.00%> (+4.11%)	4.00 <0.00> (ø)
...n/kotlin/io/github/detekt/report/sarif/SarifDsl.kt	100.00% <100.00%> (ø)	0.00 <0.00> (ø)

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