[PHP-DEV] array_reduce callback key

[Bilge]

Hi Internals,

I just ran into a case where I needed the array key in an array_reduce() 
callback, but I can't access it :(

So I wrote a PR to fix it: https://github.com/php/php-src/pull/14986

What do you think? Does this need an RFC?

Cheers,
Bilge