Object ranges should be inferred as Range<Object> for improved fluency

The following code fails with master:

static BigInteger iterative(final BigInteger n) {
    validateParameter(n)
    BigInteger total = 1G
    if (n > 1) { (2G..n).each{BigInteger i -> total *= i } }
    total
  }

The reason is that the inferred type of the big integer range is not Range<BigInteger> but the concrete type ObjectRange. Unfortunately, this type is not generified in the Groovy codebase and can't be without breaking binary compatibility.

As a workaround, the inferred type should be Range<BigInteger.