What is the problem the feature request solves?

DataFusion provides CaseExpr for CASE WHEN and Comet has a custom IfExpr for IF(expr, true_expr, false_expr).

IF(a, b, c) is semantically equivalent to CASE WHEN a THEN b ELSE c END, so why do we have two different implementations? We should at least have common code that is used from both, and we should upstream the IF support into DataFusion.

Describe the potential solution

No response

Additional context

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