[php-src] Issue #12435: Nové dvě funkce array_first() a array_last()

Issue: https://github.com/php/php-src/issues/12435 Author: dg ### Description PHP lacks two very basic functions for working with arrays: - array_first() returning the first element of an array (or null) - array_last() returning the last element of the array (or null) While PHP has functions that return the first and last keys (array_key_first() and array_key_last()), it does not have more useful functions for values. Thus, programmers "abuse" the reset() and end() functions for this purpose. The problem is that: - these functions are used to move the internal pointer in the array - which is why they have a name that is inappropriate when used in the sense of "return me the first element" - have a side effect (i.e. moving the pointer) - in the absence of an element, they return the obsolete false and not the currently expected null, which can be combined with the ?? operator - in this they differ from the similar functions array_key_first() and array_key_last()