SplitFilter should not load black/gray lists in constructor

My project uses Configuration Split to place over 2500 configuration YML files in multiple module directories. With this in place, I found that most drush commands would take about 30 seconds to execute. I traced it to the calculation of the blacklist and graylist in SplitFilter's constructor:

 
  public function __construct(array $configuration, $plugin_id, $plugin_definition, ConfigManagerInterface $manager, StorageInterface $secondary = NULL) {
    parent::__construct($configuration, $plugin_id, $plugin_definition);
    $this->manager = $manager;
    $this->secondaryStorage = $secondary;
    $this->calculateBlacklist();
    $this->calculateGraylist();
  }

These object members are not needed until used by other methods, so I propose creating two 'get' methods which calculate these lists when needed. This restores drush to normal performance.