Deprecate text metrics

[SkafteNicki]

What does this PR do?

Deprecate RougeMetric and BleuScore in favour of their counterparts introduced in version 0.5 of torchmetrics.

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 your PR does only one thing, instead of bundling different changes together?
• Did you make sure to update the documentation with your changes?
• Did you write any new necessary tests? [not needed for typos/docs]
• Did you verify new and existing tests pass locally with your changes?
• If you made a notable change (that affects users), did you update the CHANGELOG?

PR review

• Is this pull request ready for review? (if not, please submit in draft mode)

Anyone in the community is free to review the PR once the tests have passed.
If we didn't discuss your PR in Github issues there's a high chance it will not be merged.

Did you have fun?

Make sure you had fun coding 🙃

[pep8speaks]

Hello @SkafteNicki! Thanks for updating this PR.

There are currently no PEP 8 issues detected in this Pull Request. Cheers! 🍻

Comment last updated at 2021-08-11 10:10:53 UTC

[codecov]

Codecov Report

Merging #648 (2e4c02c) into master (7634dde) will decrease coverage by 0.10%.
The diff coverage is 88.23%.

@@            Coverage Diff             @@
##           master     #648      +/-   ##
==========================================
- Coverage   88.41%   88.31%   -0.11%     
==========================================
  Files         243      242       -1     
  Lines       13025    12922     -103     
==========================================
- Hits        11516    11412     -104     
- Misses       1509     1510       +1     

Flag	Coverage Δ
unittests	88.31% <88.23%> (-0.11%)	⬇️

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

Impacted Files	Coverage Δ
flash/text/question_answering/model.py	91.03% <ø> (ø)
flash/text/seq2seq/core/metrics.py	86.66% <84.61%> (-12.41%)	⬇️
flash/core/utilities/imports.py	91.04% <100.00%> (ø)
flash/text/seq2seq/summarization/model.py	80.00% <100.00%> (ø)
flash/text/seq2seq/translation/model.py	75.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 7634dde...2e4c02c. Read the comment docs.

[Borda]

Let's inherit the deprecated metrics from the targer TM metric and do simple arguments mapping, see what we have in PL v1.4

[akihironitta]

Referred to Lightning-AI/pytorch-lightning#6515 and PL v1.4.0 for the last few commits I pushed. Feel free to revert the change back if not needed :]

[ethanwharris]

LGTM 😃