Issue #2961380 by alexpott, manishsaharan, borisson_, kim.pepper, znerol: Support IteratorArgument in \Drupal\Component\DependencyInjection\Dumper\OptimizedPhpArrayDumper::dumpValue

Issue #3108020 by bonrita, Cyberwolf, sagarchauhan, znerol, borisson_: Support ServiceClosureArgument in \Drupal\Component\DependencyInjection\Dumper\OptimizedPhpArrayDumper::dumpValue

Issue #2243439 by amitgoyal, jonreid, mark.labrecque, mpv, pwolanin, scor, cilefen, sun: Fix up docs about config file/database locations in settings.php and READMEs in directories