Move KtFileContent to FileParsingRule

[BraisGabin]

KtFileContent is used for more rules than MaxLineLength so it should not be declared in that file. FileParsingRule.kt is a better place because is where the constructor of that class is called.

[codecov]

Codecov Report

Merging #3173 into master will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master    #3173      +/-   ##
============================================
+ Coverage     79.45%   79.50%   +0.04%     
- Complexity     2592     2598       +6     
============================================
  Files           437      438       +1     
  Lines          7871     7914      +43     
  Branches       1501     1509       +8     
============================================
+ Hits           6254     6292      +38     
- Misses          820      821       +1     
- Partials        797      801       +4     

Impacted Files	Coverage Δ	Complexity Δ
...lab/arturbosch/detekt/rules/style/MaxLineLength.kt	78.78% <ø> (-0.63%)	22.00 <0.00> (ø)
...b/arturbosch/detekt/rules/style/FileParsingRule.kt	100.00% <100.00%> (ø)	2.00 <0.00> (ø)
...bosch/detekt/formatting/KtLintLineColCalculator.kt	88.09% <0.00%> (ø)	6.00% <0.00%> (?%)
...lab/arturbosch/detekt/formatting/FormattingRule.kt	96.42% <0.00%> (+0.13%)	11.00% <0.00%> (ø%)

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