Consider Using The Splat Operator In The Merge Plugin

Hello

Thank you for all the great process plugins in this module. I used the merge plugin regulatory and noticed that it currently used array_merge within a foreach loop.

I use the EA Performance plugin for PHPStorm and one of their recommendations is to use the splat operator outside of the loop instead.

The performance gains time wise and memory wise are minimal but every little bit helps. The splat operator is available in PHP 5.6+ as well so Drupal 8 is safe in that regard.