Changeset 52038 for trunk/tests/phpunit/tests/compat/arrayKeyFirst.php

General: Introduce polyfills for array_key_first() and array_key_last() added in PHP 7.3.0.

PHP 7.3.0 introduced two new functions: array_key_first() and array_key_last(). These two functions return the first and last key of each array respectively, without affecting the internal state of the array.

The polyfills make these two functions available for use in Core on PHP versions less than 7.3.0.

Ref:

• PHP RFC ​https://wiki.php.net/rfc/array_key_first_last
• PHP manual array_key_first() ​https://www.php.net/manual/en/function.array-key-first.php
• PHP manual array_key_last() ​https://www.php.net/manual/en/function.array-key-last.php

Props desrosj, pbearne, costdev, hellofromTonya, ayeshrajans, manzoorwanijk, audrasjb, sergeybiryukov.
Fixes #45055.