Improve XmlBrowseViewBase scrolling boundaries and behaviour

 - Better restrictions on scroll position, fixing FWNX-863.
 - Better ScrollBar Maximum for improved fitting of content into
   display area. A better fix for LT-13765 than 4d6e480.
 - Improve ScrollBar LargeChange and SmallChange values.

Change-Id: I2b9863127f109726d882fa716f17c860238712b2