Fix array_udiff_assoc() and array_uintersect_assoc() clobbering the user comparison callback - #24453

array_udiff_assoc() and array_uintersect_assoc() parse the callback straight into BG(user_compare_fci) and never restore the previous value, unlike the other array_u*() functions. A comparison callback that calls one of them is replaced by the inner callback for the rest of the sort.

Split out of #24426, where the review pointed out these two functions.

To reproduce on PHP 8.4

<?php
$sorted = [3, 1, 2];
usort($sorted, function ($a, $b) {
    echo "outer\n";
    array_udiff_assoc([1], [1], function ($x, $y) { echo "inner\n"; return $x <=> $y; });
    return $a <=> $b;
});

Before: outer inner inner inner (the outer comparator is replaced after the first call)

After: outer inner outer inner outer inner