Introduced in PHP 7.3. I used it to replace reset()/end() followed by
key() where the return value of reset() is not captured and internal
pointer iteration is not locally occuring.
I also used it in a couple of places when reset() is absent but
array_key_first() is semantically desired.
Change-Id: I750d3fa71420cbdca5fb00d82ac5ca40821769d4