and rename them based on the phases.

SERVER-101233 split resharding_coordinator.cpp into resharding_coordinator_part_1.cpp ~ resharding_coordinator_part_4.cpp. One way to break down the resharding coordinator is to refactor each phases into their own classes, but this will take time and effort and now that the file has been split we should try to group the code logically as a short term solution to make it easier to navigate the code.