Implement LazyListBox based on IntersectionObserver

[ashklianko]

Implement IntersectionObserver for a LazyListBox.
Native JS code will eliminate lots of our error-prone code that supposed to trigger lazy load when bottom of scrollable area is reached.
Last added to the LazyListBox element will be observed to track when it is in the viewport of it's scrollable container.
Inheritors will need to provide scrollable container to be used. Ineritors will be able to override IntersectionObserver options (rootMargin, threshold etc.)
LazyListBox inheritors will need to define themselves what to do when lazy load is invoked.
If this approach is OK then can modyfy treegrid's postload (using setInterval for constant checks) with IntersectionObserver