Make Entity.ktElement no nullable

[BraisGabin]

There is not a good reason to keep Entity.ktElement nullable. It just make the API messier and provide no value.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.76%. Comparing base (f92f8ab) to head (2326ebd).

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #7259   +/-   ##
=========================================
  Coverage     84.76%   84.76%           
+ Complexity     3992     3991    -1     
=========================================
  Files           578      578           
  Lines         12026    12022    -4     
  Branches       2477     2469    -8     
=========================================
- Hits          10194    10191    -3     
  Misses          606      606           
+ Partials       1226     1225    -1     

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[3flex]

This might not be a good idea:

1. Not all rule violations relate to a KtElement, for example trailing whitespace (whitespace is represented by a PsiElement)
2. Rule violations like MaxLineLength can include multiple KtElements

I haven't looked into it, but do we actually need to include the KtElement in the Entity at all? A location, signature and location should be enough to report on issues.

[BraisGabin]

... do we actually need to include the KtElement in the Entity at all? A location, signature and location should be enough to report on issues.

We do. To implement the suppression feature. If KtElement is null the suppression doesn't work.

Comments were partially addressed, need to re-review