Add support for multipage TIFF images to QTiffHandler

Allows multipage TIFF images to be read via QImageReader::jumpToImage
and QImageReader::jumpNextToImage.

[ChangeLog][QtGui][QImageReader] Support multipage TIFF images through
QImageReader

Change-Id: Id6ac68b75500148e51be11eff3d296c929d2d95c
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>