standardize log_dir for loggers

[awaelchli]

What does this PR do?

Fixes #7542

logger.log_dir and trainer.log_dir was not consistently pointing to the experiment folder. It means user code cannot be logger agnostic and also the CLI has no fixed place where config files land. This PR introduces logger.experiment_dir for all loggers and deprecates the old logger.log_dir property.

TODO:

• update tests
• deprecation message

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[codecov]

Codecov Report

Merging #7543 (5b019e8) into master (2d682fa) will decrease coverage by 5%.
The diff coverage is 98%.

❗ Current head 5b019e8 differs from pull request most recent head d571d04. Consider uploading reports for the commit d571d04 to get more accurate results

@@           Coverage Diff            @@
##           master   #7543     +/-   ##
========================================
- Coverage      92%     88%     -5%     
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  Files         217     202     -15     
  Lines       14328   13082   -1246     
========================================
- Hits        13222   11481   -1741     
- Misses       1106    1601    +495     

[pep8speaks]

Hello @awaelchli! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

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

Comment last updated at 2021-07-24 17:12:49 UTC

[ananthsub]

this broadcast should be done once so we're not calling this on every property access

[tshu-w]

ping for this 👀

[tshu-w]

ping for this 👀 I still cannot use other loggers with CLI.