Standardize positional datamodule and argument names

[carmocca]

What does this PR do?

Fixes #7425

1. DataLoader typing
2. Consistent argument names
3. Consistent support for DataModule as the second positional argument

I guess these 3 things could be split. Kept them together for convenience.

Question

Should we change the dataloader arguments to singular instead of plural?

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[pep8speaks]

Hello @carmocca! Thanks for updating this PR.

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

Comment last updated at 2021-06-15 11:26:10 UTC

[codecov]

Codecov Report

Merging #7431 (8950e11) into master (024cf23) will decrease coverage by 0%.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master   #7431   +/-   ##
======================================
- Coverage      92%     91%   -0%     
======================================
  Files         203     203           
  Lines       13151   13173   +22     
======================================
- Hits        12042   12026   -16     
- Misses       1109    1147   +38     

[Borda]

consider using this wrapper https://github.com/Borda/pyDeprecate#self-argument-mapping
with mapping to rank zero https://github.com/PyTorchLightning/pytorch-lightning/blob/96433d03ea6323adea9a822a8222f7ea7ffba99b/pytorch_lightning/metrics/utils.py#L32

[tchaton]

LGTM !