Issue #3518123 by dydave: Refactored method 'flushJsCss' with...

https://www.drupal.org/project/admin_toolbar/issues/3518123

Admin Toolbar Tools:
Refactored method flushJsCss with backwardsCompatibleCall to support deprecated _drupal_flush_css_js for versions below core:10.2.

PHPSTAN: Ignored error message:

Unable to resolve the template type Deprecated in call to method static method Drupal\Component\Utility\DeprecationHelper::backwardsCompatibleCall()