[UX/UI] Bookreader selected page adjustments

[UcDust]

During OS team testing, it was noted that the selected page indicator, like page 2 of 3, when in 2 page mode, can be misleading. Items with an odd number of pages have the first page on the right side of the viewer, so when viewing the last 2 pages of the item, the range slider stays at the position before the last, and the label makes it seem that there is another page to scroll to.

Instead, we'd like to update the label to show the range of selected pages, as well as to set the slider position to be the last position, if viewing the last 2 pages-