The query planner is able to optimize IN operators on virtual tables
even if the xBestIndex method does not set the
sqlite3_index_constraint_usage.omit flag of the
virtual table column to the left of the IN operator.
The query planner now does a better job of optimizing virtual table
accesses in a 3-way or higher join where constraints on the virtual
table are split across two or more other tables of the join.