Make findings a List<Finding2> instead of a Map<RuleSet.Id, List<Finding2>>

[BraisGabin]

This change simplifies a lot Detektion and all their related code. We were using Map<RuleSet.Id, List<Finding2>> as the only way to carry the RuleSet.Id of a finding. Now we have that information inside Finding2 so we don't need this Map anymore.

You can see that a lot of reports were just flattening that map because they don't need it. And the ones that really need it now it is as simple as add a findings.groupBy { it.rule.ruleSetId }.

We should even check if we need to sort the findings at the core level. But I didn't want to touch that part right now.

[codecov]

Codecov Report

Attention: Patch coverage is 80.55556% with 7 lines in your changes are missing coverage. Please review.

Project coverage is 83.80%. Comparing base (f0e7d91) to head (5812e77).

Files	Patch %	Lines
...otlin/io/gitlab/arturbosch/detekt/core/Analyzer.kt	54.54%	3 Missing and 2 partials ⚠️
...gitlab/arturbosch/detekt/api/ReportingExtension.kt	0.00%	1 Missing ⚠️
...tlab/arturbosch/detekt/core/reporting/Reporting.kt	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #6884      +/-   ##
============================================
- Coverage     83.89%   83.80%   -0.10%     
+ Complexity     3939     3930       -9     
============================================
  Files           577      577              
  Lines         12109    12070      -39     
  Branches       2485     2476       -9     
============================================
- Hits          10159    10115      -44     
- Misses          722      729       +7     
+ Partials       1228     1226       -2     

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[cortinico]

Amazing cleanup! Just one minor nit