Run plugin closure before on_before_optimizer_step [1/2]

[carmocca]

What does this PR do?

Fixes:

• The lambda closure should run before on_before_optimizer_step
• The lambda closure should also be run for manual optimization
• The optimizer update needs to always run regardless of the skipped_backward value during manual optimization. This is because the closure is not required to return a value in that case.
• Extend coverage of backward skipping for Apex and DeepSpeed.

Part 2: #9287

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

None

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[codecov]

Codecov Report

Merging #9288 (2db195d) into master (98e2f56) will increase coverage by 0%.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master   #9288   +/-   ##
======================================
  Coverage      92%     92%           
======================================
  Files         178     178           
  Lines       14895   14899    +4     
======================================
+ Hits        13748   13752    +4     
  Misses       1147    1147           

[SeanNaren]

Thanks @carmocca!