Generic Struct Cycles Analyzer

This analyzer catches a few cases where the compiler doesn't error on a field or auto-property declaration that would cause a TypeLoadException at runtime. PR's are welcome!

An example of an issue this catches:

struct S0<T>
{
}

struct S1
{
    public S0<S1> Field;
}

Despite the fact that S0<T> doesn't actually have any instance fields of T, the runtime still throws a TypeLoadException loading S1 as it thinks it's a struct layout cycle, and currently Microsoft's compiler doesn't report this issue at all. So, to help this issue, this analyzer reports these and similar circumstances involving generic structs.