Write a function that makes the first number as large as possible by swapping out its digits for digits in the second number.
To illustrate:
maxPossible(9328, 456) ➞ 9658
// 9658 is the largest possible number built from swaps from 456.
// 3 replaced with 6 and 2 replaced with 5.
maxPossible(523, 76) ➞ 763
maxPossible(9132, 5564) ➞ 9655
maxPossible(8732, 91255) ➞ 9755