Unify checkpoint load paths [redo #9693]

[jjenniferdai]

What does this PR do?

Fixes #9405
rebase/redo #9693

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[rohitgr7]

LGTM!

[codecov]

Codecov Report

Merging #10061 (e8932a1) into master (76081fb) will decrease coverage by 4%.
The diff coverage is 100%.

@@           Coverage Diff            @@
##           master   #10061    +/-   ##
========================================
- Coverage      93%      89%    -4%     
========================================
  Files         182      182            
  Lines       16157    16140    -17     
========================================
- Hits        14947    14314   -633     
- Misses       1210     1826   +616