Move FigureRegion to the isaac.dos.content package

[jsharkey13]

This is a DO, and so should be in this package. Added a comment in the JavaDoc to clarify why this class does not need a DTO mapping, since this has confused several of us lately.

This change will have no impact on the format of content or JSON.

Also fix some Checkstyle warnings 🙈

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 36.77%. Comparing base (2fc0af0) to head (4d5c5cd).
⚠️ Report is 48 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #749   +/-   ##
=======================================
  Coverage   36.77%   36.77%           
=======================================
  Files         545      545           
  Lines       23692    23692           
  Branches     2832     2832           
=======================================
  Hits         8712     8712           
  Misses      14102    14102           
  Partials      878      878           

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