GetTombstonedAnnotationsForBook now also returns each tombstone's
start_position/end_position and epubcfi_start/end (note: position/
epubcfi_location, bookmark: position/cfi_position), so serving code
can resolve a device-native locator for deletions of web-created
annotations, whose device_sync_data carries no pos0.
john-okeefe
0670d904a0