clone IndexList for perf modifications

[jeffwashington]

Problem

see: #32423

Summary of Changes

fork IndexList to prepare to add a method

Fixes #

[codecov]

Codecov Report

Merging #32501 (c57e43c) into master (bb407d2) will increase coverage by 0.0%.
Report is 3 commits behind head on master.
The diff coverage is n/a.

❗ Current head c57e43c differs from pull request most recent head 889c2db. Consider uploading reports for the commit 889c2db to get more accurate results

@@            Coverage Diff            @@
##           master   #32501     +/-   ##
=========================================
  Coverage    82.0%    82.1%             
=========================================
  Files         785      778      -7     
  Lines      211077   210055   -1022     
=========================================
- Hits       173187   172486    -701     
+ Misses      37890    37569    -321