Creates a collection of planner factories.
The collection must have at least one factory, and each factory must
create a planner. If the collection has more than one planner, Calcite will
try each planner in turn.
One of the things you can do with this mechanism is to try a simpler,
faster, planner with a smaller rule set first, then fall back to a more
complex planner for complex and costly queries.
The default implementation returns a factory that calls
#createPlanner(org.apache.calcite.jdbc.CalcitePrepare.Context).