[Feature] Support KID

[LeoXing1996]

Feature:

• Support KID
• Support Metric to use the full dataset

TODO:

• Update activation to extracted inception state files
• Support download inception state files by URL (After merge [Feature] Support download inception state from url #233 )

[codecov]

Codecov Report

Merging #234 (ead647e) into master (c355edb) will increase coverage by 0.02%.
The diff coverage is 62.06%.

@@            Coverage Diff             @@
##           master     #234      +/-   ##
==========================================
+ Coverage   76.71%   76.73%   +0.02%     
==========================================
  Files         130      130              
  Lines        9421     9530     +109     
  Branches     1899     1922      +23     
==========================================
+ Hits         7227     7313      +86     
- Misses       1728     1744      +16     
- Partials      466      473       +7     

Flag	Coverage Δ
unittests	76.73% <62.06%> (+0.02%)	⬆️

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

Impacted Files	Coverage Δ
mmgen/core/evaluation/evaluation.py	7.76% <0.00%> (-0.36%)	⬇️
mmgen/core/evaluation/metrics.py	76.27% <78.26%> (+0.75%)	⬆️
...chitectures/stylegan/generator_discriminator_v2.py	87.77% <0.00%> (+1.11%)	⬆️
mmgen/models/architectures/fid_inception.py	94.44% <0.00%> (+2.38%)	⬆️

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