[Feature] add kitti AP40 evaluation metric

[ZCMax]

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Modification

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[codecov]

Codecov Report

Merging #914 (7156b85) into master (075f444) will decrease coverage by 0.17%.
The diff coverage is 1.92%.

❗ Current head 7156b85 differs from pull request most recent head d66bffd. Consider uploading reports for the commit d66bffd to get more accurate results

@@            Coverage Diff             @@
##           master     #914      +/-   ##
==========================================
- Coverage   49.33%   49.15%   -0.18%     
==========================================
  Files         210      210              
  Lines       16021    16081      +60     
  Branches     2556     2577      +21     
==========================================
+ Hits         7904     7905       +1     
- Misses       7614     7673      +59     
  Partials      503      503              

Flag	Coverage Δ
unittests	49.15% <1.92%> (-0.18%)	⬇️

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Impacted Files	Coverage Δ
mmdet3d/core/evaluation/kitti_utils/eval.py	29.04% <1.92%> (-3.19%)	⬇️

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[Tai-Wang]

Just need to rollback the changed variable names