Drupal 11 compatibility

Merged, and as @berdir noted for this to really work you need to patch manually Bootstrap 4 util.js to be compatible with Drupal 11 jQuery 4 version, something like:

-      var maxMajor = 4;
+      var maxMajor = 5;

However you should probably not do this, we need this internally so we can more easily start working on the Bootstrap 5 port and test stuff.