Avoid pushdown of negative position for element_at as subfield pruning for array

[jp-sivaprasad]

Description

Currently negative array subscript (for example, an array index of -2, for element_at ) is pushed down as subfield pruning, and worker is not sanity checking against it causing IllegalArgumentException
(Issue : #22690)

The fix is to avoid pushing down negative position for element_at for array, in PushdownSubfields.toSubfield()

Motivation and Context

Impact

Test Plan

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== RELEASE NOTES ==

General Changes
* Avoid pushdown of negative position for element_at for array  :pr:`23479`

[linux-foundation-easycla]

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[tdcmeehan]

Please reword commit message per our guidelines in CONTRIBUTING. Perhaps Avoid pushdown of negative position for element_at

[tdcmeehan]

Please add a release note @jp-sivaprasad