Follow-up to #2368: Improved docs and tests for Crops with padding

[vfdev-5]

Description:

This PR is a follow-up to #2368 with improved docs and tests for

• RandomCrop: crop with padding using all commonly supported modes
• pad in functional and functional_tensor

Additionally, make tests check results for class transforms between tensor and image.

[codecov]

Codecov Report

Merging #2371 into master will decrease coverage by 0.05%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2371      +/-   ##
==========================================
- Coverage   68.59%   68.54%   -0.06%     
==========================================
  Files          93       93              
  Lines        7713     7719       +6     
  Branches     1196     1199       +3     
==========================================
  Hits         5291     5291              
- Misses       2077     2080       +3     
- Partials      345      348       +3     

Impacted Files	Coverage Δ
torchvision/transforms/functional.py	78.05% <ø> (ø)
torchvision/transforms/functional_tensor.py	62.85% <ø> (-2.24%)	⬇️
torchvision/transforms/transforms.py	77.48% <ø> (ø)

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[fmassa]

Thanks a lot Victor!