[Feature]: Support Condinst

[JosonChan1998]

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Motivation

Add Condition instance segmentation methods. The results are listed below:

MS_R_50_1x	box AP	mask AP
origin	39.7	35.7
ours(12e)	39.6	35.2
ours(90k)	39.9	35.5

The reproduction results are still a little behind, probably because there are more iterations in detectron2.

Modification

1. configs/condinst
2. mmdet/models/detectors/condinst.py
3. mmdet/models/dense_heads/condinst_head.py
4. mmdet/models/utils/misc.py

BC-breaking (Optional)

Does the modification introduce changes that break the backward-compatibility of the downstream repos?
If so, please describe how it breaks the compatibility and how the downstream projects should modify their code to keep compatibility with this PR.

Use cases (Optional)

If this PR introduces a new feature, it is better to list some use cases here, and update the documentation.

Checklist

1. Pre-commit or other linting tools are used to fix the potential lint issues.
2. The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
3. If the modification has potential influence on downstream projects, this PR should be tested with downstream projects, like MMDet or MMCls.
4. The documentation has been modified accordingly, like docstring or example tutorials.

[CLAassistant]

All committers have signed the CLA.

[JosonChan1998]

@RangiLyu Hi~ Any progress?

[RangiLyu]

The reproduction results are still a little behind, probably because there are more iterations in detectron2.

Is the precision of the inference aligned? Can this implementation get the same box and mask AP with a converted weight from the original version?

[hhaAndroid]

@JosonChan1998 I think this PR is very well. Just need to add unit tests, I have no other comments.

[RangiLyu]

The code looks good to me now. Would you like to write the README.md file?

[RangiLyu]

Remember to use polygon masks. And after this change, the config file name should be renamed to condinst_r50_fpn_ms-poly-90k_coco.py

[JosonChan1998]

Remember to use polygon masks. And after this change, the config file name should be renamed to condinst_r50_fpn_ms-poly-90k_coco.py

Done.

The base branch was changed.