Function: LibSwiftyPluginView::is_required_plugin_active

Is this plugin with slug $plugin_name active?
Keep track of earlier checks to improve speed

Example:

if( LibSwiftyPluginView::is_required_plugin_active( 'si-contact-form' ) ) {
  // do something with this plugin
} else {
  return apply_filters( 'swifty_plugin_not_active', 'Fast Secure Contact Form' );
}