f0db870822 added support for tree-views to remember state, but only to
remember their custom height for the start. This change makes the scroll
offset be remembered too.
Not remembering the scroll offset can be very annoying in some cases,
e.g. when working with bone collections and changing the active tab in
the properties editor often. In realistic, non-trivial bone collection
set ups this can lead to a lot of repeated scrolling.
Cherry-picked for the 4.4 release since this solves a real usability
issue with trivial changes. Discussed with Thomas and others.
ed0d01c5af