add more projection pushdown slt tests (#20015)

Adds more interesting test cases extracted from
#19538

The reasoning is that it's (1) better to split the additional tests out
from that PR to make that PR easier to review and (2) it's a good thing
to document current behavior with complex edge cases like these, so even
if that PR doesn't get merged there is still value in having these as
regression tests.

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Co-authored-by: Claude Haiku 4.5 <noreply@anthropic.com>

Author: adriangb