Previous fixes for operations with out-of-order timestamps involved changing the effective start timestamp for an operation to match when it has an earlier stop timestamp. The same needs to be done for the (new) start_durable_ts field: when operations are done with out-of-order timestamps, it should be made to match stop_durable_ts.

Otherwise, an assertion can during reconciliation because start_ts == WT_TS_NONE but start_durable_ts != WT_TS_NONE.