Audit uses of duplicate bucket iteration code

[sisuresh]

There are a couple parts of core that iterate over the bucket list that should be able to share code. We should audit core to find these uses. Here are a couple -

1. getLiveBucketListBalanceForAsset from Add command line util to calculate total supply of assets and validate total coins for XLM. #4983 can use loadCompleteBucketListStateHelper, although this will load all of live state into memory. We could avoid this by changing the helper to loop over buckets from new->old instead of old->new.
2. dumpStateArchivalStatistics