feat: map an expression even if it would change the meaning of the operation.

[rodrigoreis]

Creates a feature to allows map an expression even if it would change the meaning of the operation.

It's avoid the following:

System.InvalidOperationException: Rewriting child expression from type to type is not allowed, because it would change the meaning of the operation. If this is intentional, override 'VisitUnary' and change it to allow this rewrite.

[BlaiseD]

Maybe a better fix would be to just replace the VisitUnary method with:

        protected override Expression VisitUnary(UnaryExpression node)
        {
            return DoVisitUnary(Visit(node.Operand));

            Expression DoVisitUnary(Expression updated)
            {
                if (updated != node.Operand)
                    return node.Update(updated);

                return node;
            }
        }

The existing processing would them be handled by VisitLambda and VisitConstant.

[BlaiseD]

Opened Isuue #37 to track this.

[BlaiseD]

Closing this in favor of PR #38 - I've described the fix in earlier comments.