Handle case when shortenedLoggerNameLength is set to 0 (zero)

[brenuart]

ClassNameOnlyAbbreviator should be used instead of TargetLengthBasedClassNameAbbreviator when the desired length is set to 0.

Closes #747

[codecov]

Codecov Report

Merging #748 (fa64615) into main (0e770cb) will increase coverage by 0.07%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##               main     #748      +/-   ##
============================================
+ Coverage     70.45%   70.53%   +0.07%     
- Complexity     1223     1228       +5     
============================================
  Files           162      162              
  Lines          4719     4728       +9     
  Branches        481      481              
============================================
+ Hits           3325     3335      +10     
+ Misses         1147     1146       -1     
  Partials        247      247              

Impacted Files	Coverage Δ
...composite/loggingevent/LoggerNameJsonProvider.java	95.83% <100.00%> (+15.83%)	⬆️
...h/logback/composite/FastISOTimestampFormatter.java	95.23% <0.00%> (-1.20%)	⬇️

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