S-Expr: Vars are emitted instead of equivalent terms

[ashiven]

• This is a bug in the sexpr emitter

fun extern tile1d(n1 n2: Nat): Nat =
    let test = %core.nat.mul (n1, n2);
    return test;

• In this example, the variable of the lambda is equivalent to the term (n1, n2) and instead of (tuple n1 n2) the sexpr emitter instead emits the name of the lambdas' variable(with some gid): _12345