feat(html): the viewer states whether a click opens a sheet cell

[andiwand]

Follow-up to #908, which asks the pointer whether a click edits. The pointer is a guess, and it is wrong where it matters: an android WebView reports (pointer: coarse) as false on an emulator, so the tap-to-edit that PR is for did not happen there at all - measured on a Pixel 6 Pro AVD, matchMedia("(pointer: coarse)").matches === false with editing enabled and a tap landing on the cell.

The viewer knows its input model; the library is guessing at it. So odr.editing.setSheetOptions({editOnClick}) states it, the way odr.annotation.setOptions already states the marking gestures. Unstated (null), the pointer answers exactly as it does today, so nothing changes for a viewer that says nothing.

odr.editing.setSheetOptions({ editOnClick: true });   // a phone app
odr.editing.getSheetOptions();                        // {editOnClick: true}
odr.editing.setSheetOptions({ nope: 1 });             // throws

Checked

test/browser/sheet/editing.html: 77 checks, none failing, seven of them new - the default asks the pointer, stated off a click opens nothing while the double click still works, stated on one click opens the cell with its text and pins it, and an unknown option throws.