Find the type at a given index in a list of types.
Declared in <llvm/ADT/STLExtras.h>
<llvm/ADT/STLExtras.h>
template< size_t I, typename... Ts> using TypeAtIndex = std::tuple_element_t<I, std::tuple<Ts...>>;
TypeAtIndex<I, Ts...> is the type at index I in Ts.