Not valid to convert Aggregate with on empty to empty if its GROUP BY key is empty

It it not valid to convert Aggregate with on empty to empty if its GROUP BY key is empty. Consider the following SQL:

SELECT count(*) FROM emp WHERE FALSE

Even though the input is empty, the output is one row.

Fix affects PruneEmptyRules.AGGREGATE_INSTANCE.

Also, add a RelBuilderFactory argument to all rules in PruneEmptyRules and call RelBuilder.empty rather than LogicalValues.createEmpty.