"where am I" needs reviewing to fix inconsistencies with interactive progression bar

[danielweck]

follow-up to: https://github.com/edrlab/thorium-reader/pull/2326

local vs. global progression units, differentiation between audiobooks, EPUB FXL vs. reflow (which can be spine-item level, or publication-wide), EPUB reflow paginated vs. scroll, PDF, Divina