[libview] Split EvPixbufCache into dynamic and static data

Dynamic page data (page surfaces and selections) that depend on current
scale/rotation, keep in EvPixbufCache with the current cache approach.
Static page data (links, annots, images, text and forms) that don't
depend on current scale/rotation, have been moved to EvPageCache and they
are never removed from the cache.
Fixes bgo#602405.