Deprecate process_position from the Trainer constructor

[kaushikb11]

What does this PR do?

Fixes #8968

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[tchaton]

LGTM !

[codecov]

Codecov Report

Merging #9222 (7ec5cb7) into master (f6614b3) will increase coverage by 0%.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master   #9222   +/-   ##
======================================
  Coverage      92%     92%           
======================================
  Files         176     176           
  Lines       14805   14806    +1     
======================================
+ Hits        13658   13659    +1     
  Misses       1147    1147           

[ananthsub]

thanks @kaushikb11 !