Refactor: move RowGroupPredicateBuilder into its own module, rename to PruningPredicateBuilder (#365)

* Move row group pruning logic into pruning.rs

* Rename RowGroup Predicates --> Pruning Predicates, touch up comments

* add rat

* Remove commented out println! and code

* use .any instead of filter/count

Author: alamb

datafusion/src/physical_optimizer/mod.rs

@@ -21,4 +21,5 @@
 pub mod coalesce_batches;
 pub mod merge_exec;
 pub mod optimizer;
+pub mod pruning;
 pub mod repartition;