Optimizer rule `FilterNullJoinKeys` causes null-aware joins to return incorrect results

[AdamGS]

Describe the bug

The optimizer rule FilterNullJoinKeys doesn't take null-awarness into account, which can cause it to transform the logical plan in an invalid way, returning wrong results.

This behavior isn't enabled by default, but requires setting datafusion.optimizer.filter_null_join_keys to true.

To Reproduce

From null_aware_anti_join.slt, run

set datafusion.optimizer.filter_null_join_keys = true;
SELECT * FROM outer_table WHERE id NOT IN (SELECT id FROM inner_table_with_null);

which will return incorrect results, which are different than the default datafusion.optimizer.filter_null_join_keys = false:

1 a
3 c
4 d

Expected behavior

Config changes shouldn't impact correctness

Additional context

No response