SERVER-82677 deduplicated indexes in straightforward and safe situations. The requirements were strict, for example if there's a shard key we wouldn't consider deduping. Or if the compared indexes were not plain indexes (not partial/unique/sparse/collated or any type other than btree) we would skip deduplication.

This tickets goal is to improve this logic to deduplicate in more scenarios. We should be careful to only dedup when we know the plans are guaranteed to perform equally well or one strictly worse than the other.