- added few utility functions to compensate the miss of a "central scrolled widget", as now we just fully handle (events & painting) the viewport of the scroll area
- manually scroll the overlay widgets (form widgets and video widgets) when the "area" is scrolled
All the page view functionalities should be working as usual, hopefully I should have ported everything (in case it will be fixed later).
Given that now the size page view is no more constrained by the maximum size of a QWidget (which is two orders of magnitude less than the size of an int), we can handle documents with really many pages (10k+) with hopefully no issues.
BUG: 191859
As a side effect of the QScrollArea -> QAbstractScrollArea porting, it seems that there are no more drawing glitches when in right-to-left mode.
BUG: 192636

svn path=/trunk/KDE/kdegraphics/okular/; revision=989285