Add juxt for applying multiple functions to the same arguments

[phanan]

Summary

• Adds juxt(callable ...$functions), which returns a new function that applies each given function to the same arguments and returns an array of results
• Inspired by Clojure's juxt
• Related to the existing converge(), which additionally passes results through a converging function. juxt is the simpler case where you just want the array of results.

use function Functional\juxt;

$getStats = juxt('min', 'max');
$getStats(3, 1, 5, 2); // [1, 5]

$transform = juxt('strtoupper', 'strtolower', 'strrev');
$transform('Hello'); // ['HELLO', 'hello', 'olleH']

Test plan

• Unit tests covering multiple functions, multiple arguments, array functions, closures, no functions, and single function (6 tests, 6 assertions)