As part of WT-5691, we switched to using a btree specific base_write_gen to determine whether or not to wipe transaction ids (as opposed to a connection-wide one which we used previously).

This could cause problems if we begin closing dhandles with active history since we'll wipe transaction ids . At the moment, we don't allow doing this with our dhandles but we intend to in the future so we should modify our write gen scheme to avoid this problem.