ENH: Replace "vnl/vnl_sample.h" with <random>, in Core tests

[N-Dekker]

Replaced code like randomNumber = vnl_sample_uniform(min, max) with something like:

std::mt19937                 randomNumberEngine{};
std::uniform_distribution<T> randomNumberDistribution(min, max);

randomNumber = randomNumberDistribution(randomNumberEngine);

vnl_sample_uniform is discouraged, especially because it has a global state (static data). This problem is addressed by declaring random number engines as local (non-static) variables, local to the tests that use them.

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Obviously, this modernization yields more lines of code than before. While in general, I like it better when modernization yields less code! But I can't help it 🤷 It appears fundamental to modern random number generation to declare separate "engine" and "distribution" variables, instead of just doing a single library function call.

[hjmjohnson]

Lovely!!!

[N-Dekker]

Lovely!!!

Thanks Hans! There are a few more vnl_sample_uniform calls in tests outside of the Core, but I would rather have them replaced in a separate follow-up pull request, once the current one is fully processed 😃