Support batch inference of Mask R-CNN

[hhaAndroid]

No description provided.

[codecov]

Codecov Report

Merging #4871 (1c69925) into master (ff38f20) will increase coverage by 0.18%.
The diff coverage is 85.71%.

❗ Current head 1c69925 differs from pull request most recent head b125dcf. Consider uploading reports for the commit b125dcf to get more accurate results

@@            Coverage Diff             @@
##           master    #4871      +/-   ##
==========================================
+ Coverage   65.45%   65.63%   +0.18%     
==========================================
  Files         255      255              
  Lines       19981    19987       +6     
  Branches     3398     3394       -4     
==========================================
+ Hits        13079    13119      +40     
+ Misses       6200     6165      -35     
- Partials      702      703       +1     

Flag	Coverage Δ
unittests	65.59% <82.85%> (+0.17%)	⬆️

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Impacted Files	Coverage Δ
mmdet/models/roi_heads/test_mixins.py	57.86% <85.71%> (+8.84%)	⬆️
mmdet/models/roi_heads/mask_heads/maskiou_head.py	100.00% <0.00%> (+5.37%)	⬆️
mmdet/models/roi_heads/mask_scoring_roi_head.py	87.50% <0.00%> (+32.14%)	⬆️

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[RunningLeon]

@hhaAndroid Works good for mask-rcnn exporting to ONNX

[RunningLeon]

LGTM