Pausing & Restarting read aloud should start at the page the user is on

**Problem**

I borrowed this book: https://archive.org/details/ellaenchanted00levi_1/page/117/mode/2up
Started ReadAloud on one page,
then flipped to a later section of the book and hit Play again.
It continued reading from the first page.

**Expectation**

When a user pauses read aloud on one page, then flips to another page and restarts read aloud - read aloud should start at the new page.

**Stakeholders**

@cdrini

https://webarchive.jira.com/browse/WEBDEV-3959

Reproduce the ReadAloud behavior in the BookReader using the linked Ella Enchanted page: start reading, navigate to a later page, pause, and press Play again. Trace the ReadAloud entry point and verify that restarting after navigation begins on the current page rather than the original one.

Written by the indexing model from the issue text.