Reduce the visual prominence of the page input by using a darker background and a text color that matches the rest of the toolbar icons. Darker background still indicates this is an interactive item (is an input), hopefully.
Bad commit here with too much stuff. I apologize.
This sets up two Intersection Observers: the first captures every page that is at least 30% visible inside the `.pages` container, and the second captures every page that has at least one pixel on the horizontal center line of `.pages`. Both can be arrays of integers (page index).
The "visiblePages" array is duplicated and formatted into a "formattedPages" state, which gets displayed in the toolbar.
The toolbar displays that, unless the user clicks into the page input and enters their own integer (only a single integer, no range), which can then jump the preview to that page on Enter or blur().
The Arrow 'change page' buttons jump the preview back and forth by a 'full set'.
If one page is viewed at a time, this is moved on page a time, and if 10 pages are viewed at a time it jumps the pages by 10.
Left to do: adapt the "jump editor to match preview" divider button to work with new "centerPage".
Toggles a state variable to either visible or hidden which is used to set a related class on the toolbar. The hiding is done with CSS, just reducing the width of the toolbar and the opacity of the tools.
All zoom buttons run through same handler now.
They no longer take only the delta of the current zoom and desired zoom-- they take the actual desired zoom.
calculateZoom is now calculateChange, to help get the desired delta.
Removes icons as components, uses mask-image instead.
Sets a size on the .fac icons to 1em so by default they are 1em and retain their aspect ratio.
rename the icon files for consistency.
