Rebuild hungarian assigner

[kellenf]

add focal_loss in hungarian assigner and rebuild its structure

[CLAassistant]

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[kellenf]

reviewed

[kellenf]

renamed match_costers -> match_costs

[ZwwWayne]

Please merge master to resolve conflicts.

[kellenf]

merged master

[codecov]

Codecov Report

Merging #4259 (3b7cf23) into master (23ded99) will increase coverage by 0.02%.
The diff coverage is 95.52%.

@@            Coverage Diff             @@
##           master    #4259      +/-   ##
==========================================
+ Coverage   61.79%   61.81%   +0.02%     
==========================================
  Files         237      240       +3     
  Lines       18218    18267      +49     
  Branches     3052     3058       +6     
==========================================
+ Hits        11258    11292      +34     
- Misses       6415     6427      +12     
- Partials      545      548       +3     

Flag	Coverage Δ
unittests	61.78% <95.52%> (+0.02%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
mmdet/core/bbox/match_costs/match_cost.py	93.61% <93.61%> (ø)
mmdet/core/bbox/assigners/hungarian_assigner.py	88.37% <100.00%> (-1.22%)	⬇️
mmdet/core/bbox/match_costs/__init__.py	100.00% <100.00%> (ø)
mmdet/core/bbox/match_costs/builder.py	100.00% <100.00%> (ø)
mmdet/models/dense_heads/transformer_head.py	96.39% <100.00%> (ø)
mmdet/models/roi_heads/mask_scoring_roi_head.py	55.35% <0.00%> (-32.15%)	⬇️
mmdet/models/roi_heads/mask_heads/maskiou_head.py	94.62% <0.00%> (-5.38%)	⬇️
... and 1 more

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[kellenf]

reviewed