TestIterator fails due to IEnumerator helper type not found

[manodasanW]

System.InvalidOperationException : Target type is not a projected type: System.Collections.IEnumerator.

Stack Trace: 
TypeExtensions.GetHelperType(Type type) line 103
IDynamicInterfaceCastable.GetInterfaceImplementation(RuntimeTypeHandle interfaceType) line 144
IEnumerator.MoveNext()
CustomIteratorTest.MoveNext() line 1916
TestCSharp.TestIterator() line 2595

[manodasanW]

Need to evaluate whether this needs to be converted to an IDIC interface which would be an API surface change:

CsWinRT/src/WinRT.Runtime/Projections/IEnumerable.net5.cs

Line 260 in 86d7976

class IEnumerator<T> : global::System.Collections.Generic.IEnumerator<T>, global::Windows.Foundation.Collections.IIterator<T>