Fallback when request is not available on the stack in Time service

So in our REQUEST_TIME docs we say

/**
 * Time of the current request in seconds elapsed since the Unix Epoch.
 *
 * This differs from $_SERVER['REQUEST_TIME'], which is stored as a float
 * since PHP 5.4.0. Float timestamps confuse most PHP functions
 * (including date_create()).
 *
 * @see http://php.net/manual/reserved.variables.server.php
 * @see http://php.net/manual/function.time.php
 *
 * @deprecated in drupal:8.3.0 and is removed from drupal:10.0.0.
 *   Use \Drupal::time()->getRequestTime();
 *
 * @see https://www.drupal.org/node/2785211
 */
define('REQUEST_TIME', (int) $_SERVER['REQUEST_TIME']);

But there's zero evidence of the int cast being necessary - see https://3v4l.org/VKWSU

Lol we never did revert #1209470: REQUEST_TIME is a float with microseconds on PHP 5.4

Or complete #2862477: Remove casts from REQUEST_TIME