Consider optimizations to FindIndex based on the underlying type

[Treit]

List<T> and T[] support a FindIndex operation.

The SuperLinq FindIndex operation could detect if the underlying type is one of these and call the native implementation as an optimization.

Currently, benchmarks shows that calling someList.ToList().FindIndex(predicate) is actually faster than the SuperLinq implmentation, although of course it allocates a lot more memory.

Invoking the underlying method would provide better performance and avoid the memory allocation of calling ToList() to get access to the faster FindIndex method.