Factor out classes in KidlTest that aren't part of KIDL

[MrCreosote]

... in preparation for move to java_kidl repo.

Namely, UObject and TestConfigHelper don't exist in that repo.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 65.54%. Comparing base (fe887ee) to head (91e680d).
Report is 7 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##               main      #64   +/-   ##
=========================================
  Coverage     65.54%   65.54%           
  Complexity     1410     1410           
=========================================
  Files            78       78           
  Lines          6959     6959           
  Branches       1284     1284           
=========================================
  Hits           4561     4561           
  Misses         1920     1920           
  Partials        478      478           

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