Add support of EdgeNeXt

[tonysy]

trafficstars

#930

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Motivation

Please describe the motivation of this PR and the goal you want to achieve through this PR.

Modification

Please briefly describe what modification is made in this PR.

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:

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

After PR:

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

[CLAassistant]

All committers have signed the CLA.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 92.89100% with 15 lines in your changes are missing coverage. Please review.

Project coverage is 85.60%. Comparing base (71ef7ba) to head (323f8eb). Report is 59 commits behind head on master.

Files	Patch %	Lines
mmcls/models/utils/attention.py	75.75%	6 Missing and 2 partials :warning:
mmcls/models/backbones/edgenext.py	95.20%	3 Missing and 4 partials :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #952      +/-   ##
==========================================
+ Coverage   84.57%   85.60%   +1.03%     
==========================================
  Files         134      135       +1     
  Lines        8772     8984     +212     
  Branches     1516     1550      +34     
==========================================
+ Hits         7419     7691     +272     
+ Misses       1117     1065      -52     
+ Partials      236      228       -8     

Flag	Coverage Δ
unittests	85.52% <92.89%> (+0.95%)	:arrow_up:

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