[SPARK-46632][SQL] Fix subexpression elimination when equivalent ternary expressions have different children

[zml1206]

What changes were proposed in this pull request?

Remove unexpected exception thrown in EquivalentExpressions.updateExprInMap(). Equivalent expressions may contain different children, it should happen expression not in map and useCount is -1. For example, before this PR will throw IllegalStateException

Seq((1, 2, 3), (2, 3, 4)).toDF("a", "b", "c")
      .selectExpr("case when a + b + c>3 then 1 when c + a + b>0 then 2 else 0 end as d").show()

Why are the changes needed?

Bug fix.

Does this PR introduce any user-facing change?

No.

How was this patch tested?

New unit test, before this PR will throw IllegalStateException: *** with use count: -1

Was this patch authored or co-authored using generative AI tooling?

No.

[zml1206]

cc @peter-toth @cloud-fan

[zml1206]

cc @cloud-fan Do you have time to help take a look? Thank you.

[zml1206]

@peter-toth Can this PR be merged?

[cloud-fan]

good catch! merging to master/3.5!

[zml1206]

Thank you. @cloud-fan @peter-toth