Feature suggestion: Free monadic-optional functions usable with pipe syntax.

[BenFrantzDale]

Feel free to close if you don't like this idea, but in our C++17 (soon-to-be-20) codebase, we've added namespace MonadicOptional that has pipeable transform, and_then, etc. These are cool in that (a) they let us operate on std::optional pre-C++23, but also, they let us treat pointers the same way:

using namespace MonadicOptional;
STATIC_REQUIRE(
    (std::make_unique<int>(80) //
     | and_then([](auto x) { return std::optional{x / 4}; })
     | transform([](auto x) { return x + 1; })
     | and_then([](auto x) { return std::optional{x * 2}; }))
    == std::optional{42}
);

This feels useful even after we get C++23. Would you be interested in including functionality like this in this library?