Background:
- First Pr #33245
- just decoupling scrollbar functionality from modal.js , coping the existing code as it was.
- Second Pr #33948:
- scrollbar.js: avoid to create data-bs attributes for null values
- Revisit modal, offcanvas & scrollbar tests (move scroll tests to scrollbar.spec)
This Pr:
- sets the base to support different rootElements (than body) helping #33018 and #33574
- transforms helper to class
- makes the proper changes to tests