Improve installer performance by ~20% by rebuilding the router after the entire installation is complete rather than after each module

Drupal rebuilds the router on each module installation. This is useful when adding modules once Drupal has been installed.

However, it is causing a lot of CPU cycles when Drupal is installing and the routes may be rebuilt over and over. Here's a screenshot from a Blackfire profile shaal created while we were debugging the Umami demo's installation time. The router is rebuilt 55 times before Drupal has finished being installed.

Here is the current code:

      if (!\Drupal::service('router.route_provider.lazy_builder')->hasRebuilt()) {
        // Rebuild routes after installing module. This is done here on top of
        // \Drupal\Core\Routing\RouteBuilder::destruct to not run into errors on
        // fastCGI which executes ::destruct() after the module installation
        // page was sent already.
        \Drupal::service('router.builder')->rebuild();
      }

Adding a check to drupal_installation_attempted () greatly improves the installation time. Here is the comparison when we check if Drupal is installed first

      if (!drupal_installation_attempted() && !\Drupal::service('router.route_provider.lazy_builder')->hasRebuilt()) {
        // Rebuild routes after installing module. This is done here on top of
        // \Drupal\Core\Routing\RouteBuilder::destruct to not run into errors on
        // fastCGI which executes ::destruct() after the module installation
        // page was sent already.
        \Drupal::service('router.builder')->rebuild();
      }