Fix Round()

[Lej]

This seems to fix round for the 2.5 case, but round still fails for negative numbers when MidpointRounding.ToEven causes rounding towards negative infinity.

Below expanded unit test where the case [InlineData("-3.5", -3)] fails (it is rounded to -4 when it should be rounded to -3). Note that I changed string xpath = "round(number(value))"; to string xpath = "round(xs:double(value))"; to test some edge cases.

        // https://www.w3.org/TR/xpath-functions/#func-round
        [Theory]
        [InlineData("2.51", 3)]
        [InlineData("2.5", 3)]
        [InlineData("2.4999", 2)]
        [InlineData("0", 0)]
        [InlineData("-0", 0)]
        [InlineData("-2.4999", -2)]
        [InlineData("-2.5", -2)]
        [InlineData("-2.51", -3)]
        [InlineData("-3.5", -3)]
        [InlineData("INF", double.PositiveInfinity)]
        [InlineData("-INF", double.NegativeInfinity)]
        [InlineData("NaN", double.NaN)]
        public void XPath2Evaluate_round(string value, object expected)
        {
            // Arrange
            string xpath = "round(xs:double(value))";
            var xml = new XmlDocument { InnerXml = $"<value>{value}</value>" };
            var nav = xml.CreateNavigator();

            // Act
            var result = nav.XPath2Evaluate(xpath);

            // Assert
            result.Should().Be(expected);
        }

[StefH]

@Lej Thanks for your review.

Code has been changed. Please check again.

[Lej]

@Lej Thanks for your review.

Code has been changed. Please check again.

Looks like it should work now. Had a small comment, not sure if relevant.