scrollProgress var(—prog) for dynamic non-js value update

[jesvijonathan]

We can use scrollProgress callBacks for manually handling the event but would be nice if there was support for dynamically changing
CSS var() properties so that we can add it to the elements css to update the style on scroll directly without having to create a handler for it.

• Default
  var(--jos_scroll)
  var(--jos_scroll_reverse)
• Conversions
  var(--jos_scroll_perc)
  var(--jos_scroll_deg)
• Others
  var(--jos_windowScroll)
  var(--jos_windowScroll_reverse)
  var(--jos_rootScroll_reverse)
  var(--jos_rootScroll)