C# code generation fails for UDTs with named items called `Item*`.

[cgranade]

Describe the bug

I will readily admit that no one should ever write this code, but if one defines a UDT with named items such as Item1 and Item2, compiling the generated C# code fails. In particular, compilation fails even if the affected UDT is never actually used.

To Reproduce

newtype Evil = (
    Item2: Int,
    Item1: String
);

[anpaz]

We automatically generate the Item1, Item2, etc, fields for UDTs, but I don't they are really used as all assignments happen via de-construction, so we might be able to just remove the fields.