serve_js/css BC layer in Drupal 10 is broken in 2.2.0-beta2

lisa.rae → credited dieterholvoet → .

patch attached. Will generate MR after adding tests, adding patch to allow testing by community to see if this corrects the BC issues.

Also note to self, make sure to credit @DieterHolvoet when fix is merged.

Tests have been added, tests are passing for Drupal 10.3+, failing for Drupal 11 (which is expected).