[Enhancement] Update VAN

[okotaku]

Motivation

1. Use new Architecture named series

previous arch names : 'tiny', 'small', 'base' and 'large'
previous arch names : 'b0', 'b1', 'b2' and 'b3' .....

And the 'b0' is totally equal to 'tiny'; the 'b1' is totally equal to 'small'; the 'b2' is totally equal to 'base'; the 'b3' is totally equal to 'large'.

2. Add new release weight form Official repo

• add 'b4' weight with ACC of 84.13@224
• add 'b4' ,'b5', 'b6' pre-trained weights in ImageNet-21k dataset

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: 86.14% // Head: 86.14% // No change to project coverage 👍

Coverage data is based on head (9b17acc) compared to base (ec71d07).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev    #1017   +/-   ##
=======================================
  Coverage   86.14%   86.14%           
=======================================
  Files         140      140           
  Lines        9676     9676           
  Branches     1677     1677           
=======================================
  Hits         8335     8335           
  Misses       1090     1090           
  Partials      251      251           

Flag	Coverage Δ
unittests	86.06% <ø> (ø)

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

Impacted Files	Coverage Δ
mmcls/models/backbones/van.py	96.83% <ø> (ø)
mmcls/models/utils/attention.py	96.91% <0.00%> (ø)

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[Ezra-Yu]

I think it's better to keep "tiny", "small", "large" structs before adding 'b0', 'b1' etc. This will be compatible with previous versions. You can add a new config name 'b0' but use the same checkpoint with 'tiny'.

[Ezra-Yu]

LGTM.

[okotaku]

@Ezra-Yu
Should I make this PR again for dev-1.x?
Or do you plan to incorporate PRs that have been merged into dev by the mmlab team into dev-1.x as well?

[Ezra-Yu]

@okotaku Welcome to migrating it to dev-1.x if it's convenient for you.

Yes, we plan to migrate the last few PRs on dev to dev_1.x in the remaining months of this year.

Although we need to sync master with 1.x updates in principle. But if time is not enough, supporting new features to 1.x has a higher priority. So next time, if you want to add a new feature, please add it directly to the 1.x branch.