Rename and move Result

[carmocca]

What does this PR do?

The only reason this was in core is because in ancient times, users would create and handle the results objects. This hasn't been the case anymore for a while

pytorch_lightning/core/step_result.py → pytorch_lightning/trainer/connectors/logger_connector/result.py

Part of #7631

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[codecov]

Codecov Report

Merging #7736 (7e770c0) into master (906c067) will decrease coverage by 0%.
The diff coverage is 93%.

@@          Coverage Diff           @@
##           master   #7736   +/-   ##
======================================
- Coverage      92%     92%   -0%     
======================================
  Files         199     199           
  Lines       12962   12963    +1     
======================================
- Hits        11967   11954   -13     
- Misses        995    1009   +14