[Improve] use fvcore to calculate FLOPs

[ly015]

Motivation

Ref link: open-mmlab/mmpretrain#1000

Modification

BC-breaking (Optional)

Use cases (Optional)

Checklist

Before PR:

• I have read and followed the workflow indicated in the CONTRIBUTING.md to create this PR.
• Pre-commit or linting tools indicated in CONTRIBUTING.md are used to fix the potential lint issues.
• Bug fixes are covered by unit tests, the case that causes the bug should be added in the unit tests.
• New functionalities are covered by complete unit tests. If not, please add more unit tests to ensure correctness.
• The documentation has been modified accordingly, including docstring or example tutorials.

After PR:

• CLA has been signed and all committers have signed the CLA in this PR.

[codecov]

Codecov Report

Patch coverage: 71.42% and project coverage change: -0.04 ⚠️

Comparison is base (13acbc8) 82.18% compared to head (f9bfd93) 82.14%.

❗ Current head f9bfd93 differs from pull request most recent head 3b0e12d. Consider uploading reports for the commit 3b0e12d to get more accurate results

Additional details and impacted files

@@             Coverage Diff             @@
##           dev-1.x    #2045      +/-   ##
===========================================
- Coverage    82.18%   82.14%   -0.04%     
===========================================
  Files          224      225       +1     
  Lines        13362    13379      +17     
  Branches      2265     2269       +4     
===========================================
+ Hits         10981    10990       +9     
- Misses        1867     1877      +10     
+ Partials       514      512       -2     

Flag	Coverage Δ
unittests	82.14% <71.42%> (-0.04%)	⬇️

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

Impacted Files	Coverage Δ
mmpose/models/pose_estimators/base.py	80.00% <ø> (ø)
mmpose/apis/inferencers/pose2d_inferencer.py	73.39% <50.00%> (-2.34%)	⬇️
mmpose/utils/config_utils.py	80.00% <80.00%> (ø)
...ose/apis/webcam/nodes/model_nodes/detector_node.py	82.35% <100.00%> (ø)
mmpose/utils/__init__.py	100.00% <100.00%> (ø)

... and 3 files with indirect coverage changes

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[ly015]

@Tau-J A few follow-ups:

• Please double-check the FLOPs of all rtmpose models with the updated script.
• There are mixed uses of 'rtmpose-tiny' and 'rtmpose-s/m/l' in the config names. Please select one consistent style for all configs in configs and projects/rtmpose/.

[Tau-J]

There is a newer PR of FLOPs counting open-mmlab/mmengine#779 from mmengine. Should we follow this one instead of fvcore?