[Feature] [CodeCamp #61] Add XCiT Backbone

[qingtian5]

Thanks for your contribution and we appreciate it a lot. The following instructions would make your pull request more healthy and more easily get feedback. If you do not understand some items, don't worry, just make the pull request and seek help from maintainers.

Motivation

Add the XCiT backbone and the convert weights
paper : https://arxiv.org/abs/2106.09681
code : https://github.com/facebookresearch/xcit
related to #1231

Modification

添加模型文件与配置文件

TODO

• 对齐一个模型的输出结果
• 代码规范
• 对齐所有模型的输出结果
• 对齐推理精度
• 代码重构

BC-breaking (Optional)

Does the modification introduce changes that break the backward compatibility of the downstream repositories?
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

Before PR:

• Pre-commit or other linting tools are used to fix the potential lint issues.
• Bug fixes are fully covered by unit tests, the case that causes the bug should be added in the unit tests.
• The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
• The documentation has been modified accordingly, like docstring or example tutorials.

After PR:

• If the modification has potential influence on downstream or other related projects, this PR should be tested with those projects, like MMDet or MMSeg.
• CLA has been signed and all committers have signed the CLA in this PR.

[codecov]

Codecov Report

Base: 0.02% // Head: 86.79% // Increases project coverage by +86.77% 🎉

Coverage data is based on head (f058ab0) compared to base (b8b31e9).
Patch has no changes to coverable lines.

❗ Current head f058ab0 differs from pull request most recent head f9acb81. Consider uploading reports for the commit f9acb81 to get more accurate results

Additional details and impacted files

@@             Coverage Diff              @@
##           dev-1.x    #1305       +/-   ##
============================================
+ Coverage     0.02%   86.79%   +86.77%     
============================================
  Files          121      168       +47     
  Lines         8217    13949     +5732     
  Branches      1368     2217      +849     
============================================
+ Hits             2    12107    +12105     
+ Misses        8215     1460     -6755     
- Partials         0      382      +382     

Flag	Coverage Δ
unittests	86.79% <ø> (+86.77%)	⬆️

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

Impacted Files	Coverage Δ
mmcls/datasets/transforms/compose.py
mmcls/models/backbones/mvit.py	92.46% <0.00%> (ø)
mmcls/engine/hooks/ema_hook.py	81.69% <0.00%> (ø)
mmcls/models/heads/multi_label_csra_head.py	40.54% <0.00%> (ø)
mmcls/models/utils/layer_scale.py	86.66% <0.00%> (ø)
mmcls/models/utils/norm.py	80.00% <0.00%> (ø)
mmcls/models/tta/score_tta.py	100.00% <0.00%> (ø)
mmcls/models/backbones/hornet.py	82.05% <0.00%> (ø)
mmcls/models/heads/vig_head.py	42.30% <0.00%> (ø)
mmcls/models/classifiers/hugging_face.py	25.64% <0.00%> (ø)
... and 159 more

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

☔ View full report at Codecov.
📢 Do you have feedback about the report comment? Let us know in this issue.

[mzr1996]

LGTM