While investigating the MongoDB transactions in TPCC, WiredTigerStats::WiredTigerStats method spends an excessive amount of time opening a cursor, iterating the cursor and then closing the cursor to retrieve 8 uint64_t metrics.

This ticket will add an API to WT_SESSION to memcpy the metrics out instead of using the cursor. The expectation is that memcpy is cheaper then the WT cursor API.

Will have a secondary benefit of reducing the costs to read some of the metrics for needed by PM-3268.