Function resolve_positions_to_exprs 

pub(crate) fn resolve_positions_to_exprs(
    expr: Expr,
    select_exprs: &[Expr],
) -> Result<Expr>

Given an expression that’s literal int encoding position, lookup the corresponding expression in the select_exprs list, if the index is within the bounds and it is indeed a position literal, otherwise, returns planning error. If input expression is not an int literal, returns expression as-is.