[MPS support] Make Jaccard Index working on MPS

[stancld]

What does this PR do?

Fixes #1196

• Change _bincount calculation for MPS to run for loop fallback
• Use torch.where implementation to apply absent_score instead of relying on item assignment

There's still a warning on PyTorch side (using CPU fallback for some operations; see UserWarning below), however,
no actions on our users' side are now required and the results are obtained smoothly. Calculation runs with warnings (but without errors!) both with PYTORCH_ENABLE_MPS_FALLBACK=0 and PYTORCH_ENABLE_MPS_FALLBACK=1.

/Users/stancld/miniconda3/envs/metrics/lib/python3.9/site-packages/torch/_tensor_str.py:103: UserWarning: The operator 'aten::bitwise_and.Tensor_out' is not currently supported on the MPS backend and will fall back to run on the CPU. This
 may have performance implications. (Triggered internally at  /Users/runner/work/pytorch/pytorch/pytorch/aten/src/ATen/mps/MPSFallback.mm:11.)                                                                                                
  nonzero_finite_vals = torch.masked_select(tensor_view, torch.isfinite(tensor_view) & tensor_view.ne(0))  

(tested on my M1 Mac)

Before submitting

• Was this discussed/approved via a Github issue? (no need for typos and docs improvements)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure to update the docs?
• Did you write any new necessary tests?

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[codecov]

Codecov Report

Merging #1205 (fbd9b57) into master (5bc828d) will increase coverage by 0%.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master   #1205   +/-   ##
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  Coverage      94%     94%           
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  Files         185     185           
  Lines        8407    8408    +1     
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+ Hits         7895    7896    +1     
  Misses        512     512