New port: devel/tl-expected: C++11/14/17 std::expected with functional-style extensions

Single header implementation of std::expected with functional-style extensions.

std::expected is proposed as the preferred way to represent object which will
either have an expected value, or an unexpected value giving information about
why something failed. Unfortunately, chaining together many computations which
may fail can be verbose, as error-checking code will be mixed in with the
actual programming logic. This implementation provides a number of utilities to
make coding with expected cleaner.

WWW: https://github.com/TartanLlama/expected

PR: 244550
Submitted by: Henry Hu <henry.hu.sh@gmail.com>