Add GetRandomElement helpers and cleanup tpzrand

[zach2good]

This allows:

std::vector<int> v{ 1, 2, 3, 4, 5 };
auto ptrToV = &v;

tpzrand::GetRandomElement(v);
tpzrand::GetRandomElement(ptrToV);
tpzrand::GetRandomElement({ 1, 2, 3, 4, 5 });

... on any type that has at() and size().

For the C++ nerds out there, I tried to use SFINAE to validate if passed in containers had access to at() and size(), but template voodoo isn't my speciality. I got as far as:

template <typename T, typename Enable = void>
inline constexpr bool is_container_like = false;

template <typename T>
inline constexpr bool is_container_like
<T, std::void_t<
    decltype(std::declval<T>().at()),
    decltype(std::declval<T>().size())>
> = true;

template <typename T>
static inline auto GetRandomElement(T* container)
-> std::enable_if_t<is_container_like<T>, typename T::value_type>
{
    return container->at(GetRandomNumber<std::size_t>(0U, container->size()));
}

🤷

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• that I agree to Project Topaz's Limited Contributor License Agreement, as written on this date
• that I've tested my code since the last commit in the PR, and will test after any later commits