Maintain in-page scroll position when moving between viewer tabs

[reefdog]

Steps to reproduce mild annoyance:

1. Open a document with a long page of text
2. Scroll down a bit (so the top of the current page extends beyond the top of the viewport)
3. Flip to the Text tab and scroll it down a bit as well
4. Flip back to the Document tab
5. Flip back to the Text tab

What happens: Every time you change tabs, scroll position is returned to the top of the current page.

What would be ideal: Unless the current page has changed, the viewer should maintain the old scroll position. This is particularly helpful when flipping between the Document (or Pages) view and Text, since you're often referencing the text view to check OCR accuracy and scrolling back down to the relevant bit becomes tiring.