[api] Refactor drawMask() for instance segmentation

[frankfliu]

Description

Brief description of what this PR is about

• If this change is a backward incompatible change, why must this change be made?
• Interesting edge cases to note here

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 8.16327% with 45 lines in your changes missing coverage. Please review.

Project coverage is 57.91%. Comparing base (725851b) to head (eeab075).
Report is 3 commits behind head on master.

Files	Patch %	Lines
...pencv/src/main/java/ai/djl/opencv/OpenCVImage.java	0.00%	20 Missing ⚠️
.../java/ai/djl/modality/cv/BufferedImageFactory.java	0.00%	19 Missing ⚠️
.../cv/translator/InstanceSegmentationTranslator.java	0.00%	6 Missing ⚠️

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Additional details and impacted files

@@              Coverage Diff              @@
##             master    #3304       +/-   ##
=============================================
- Coverage     72.71%   57.91%   -14.81%     
+ Complexity     7361     5757     -1604     
=============================================
  Files           677      677               
  Lines         32561    32594       +33     
  Branches       3433     3441        +8     
=============================================
- Hits          23677    18877     -4800     
- Misses         7258    12261     +5003     
+ Partials       1626     1456      -170     

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