Bump OpenCV to 4.12.0, add new constructor for FlannBasedMatcher

[rainyl]

• bump opencv to 4.12.0
• add FlannIndexParams, FlannSearchParams
• add FlannBasedMatcher.create
• fix: FlannBasedMatcher constructor #369 Not able to compile for android after version 1.3.0 #293

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 95.78947% with 8 lines in your changes missing coverage. Please review.

Project coverage is 93.40%. Comparing base (f60f745) to head (30332da).

Files with missing lines	Patch %	Lines
packages/dartcv/lib/src/features2d/features2d.dart	95.78%	8 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #370      +/-   ##
==========================================
+ Coverage   93.37%   93.40%   +0.03%     
==========================================
  Files          50       50              
  Lines       10380    10535     +155     
==========================================
+ Hits         9692     9840     +148     
- Misses        688      695       +7     

Flag	Coverage Δ
unittests	93.40% <95.78%> (+0.03%)	⬆️

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