Decorrelation Simplification Passes

[notSaranshMalik]

Problem

Some extraneous domain joins were inserted into TPCH queries due to a missing simplification rule about converting LeftJoins into InnerJoins and propagating that downward.

Summary of changes

2 new rules are added:

• The first converts left joins into inner joins when there are null rejecting predicates on the right branch
• Given inner joins, unnecessary domain joins under them are removed