Added a new check to array to see if it contains only an int based keys in natural order (from 0 to n`). Useful when we want to ensure the array is consistent (untouched) and when we want to serialize an array to json to format of [0, 1, 2] instead of object properties.
This feature doesn’t change PHP’s type system and doesn’t add new type hints.
$x = [1 => 'a', 0 => 'b'];
var_export(array_is_list($x)); // false because keys are out of order
unset($x[1]);
var_export(array_is_list($x)); // true
// Pitfalls of simpler polyfills - NAN !== NAN
$x = ['key' => 2, NAN];
unset($x['key']);
var_export($x === array_values($x)); // false because NAN !== NAN
var_export($x); // array (0 => NAN)
var_export(array_is_list($x)); // true because keys are consecutive integers starting from 0
array_is_list(new stdClass()); // throws a TypeError
array_is_list(null); // throws a TypeError
