The splitVector function is currently serving 3 different purposes:

• Provide users a way to determine bounds for parallelizing data processing, through the splitVector command
• Determine the initial split points
• Determine the auto-splitter's split points

Objective of this ticket is to extract the logic currently used by the chunk splitter - basically copy the splitVector function and "peel" the code not reached during auto splitting - into a different function to be backported with minimum effort.

This is a precondition for SERVER-55028 aimed to improve chunk splitter's split points selection policy without impacting the user-facing splitVector behavior.