Save the ResultCollection in the loops state dict

[tchaton]

What does this PR do?

This PR adds support for loading / restoring ResultCollection automatically with multiple processes from the state_dict.

Does your PR introduce any breaking changes? If yes, please list them.

No.

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[codecov]

Codecov Report

Merging #8641 (923c74b) into master (15fb320) will increase coverage by 0%.
The diff coverage is 90%.

@@          Coverage Diff           @@
##           master   #8641   +/-   ##
======================================
  Coverage      93%     93%           
======================================
  Files         167     167           
  Lines       13960   13999   +39     
======================================
+ Hits        12928   12968   +40     
+ Misses       1032    1031    -1     

[pep8speaks]

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

• In the file pytorch_lightning/loops/base.py:

Line 216:17: W503 line break before binary operator
Line 217:17: W503 line break before binary operator

Comment last updated at 2021-08-02 19:57:06 UTC

[ethanwharris]

LGTM 😃