stroke.widthPoint.set and .copy read `index` with `as_u64() as usize`:
a malformed index ("bad", -1, 1.5) was taken as no index, so set added a
new point instead of failing, and a huge one wrapped round on wasm32.
They now read it through point_indices, as remove does since #1079:
anything but an index of an existing point is "no such width point".
A null index is still no index (set adds a point).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Double-clicking a width point opens Width Point Edit (Side 1, Side 2, Total Width, a link
keeping the sides equal, Adjust Adjoining Width Points, Delete; dialog `widthPoint`, also
`ui.widthPointEdit`). Shift-click selects several width points, which drag and widen together
as one undo step; Alt-dragging a point's centre copies it (`stroke.widthPoint.copy`); dropping a
point onto another makes a discontinuous point (two points at the same t), and the stroke's
width steps there. `stroke.widthPoint.set` takes `adjustAdjoining`, keeps a discontinuous point
when only its widths change, and `stroke.widthPoint.remove` takes `indices`. Flipping a profile
along the path swaps the sides of its steps; `document.inspect` reports `widthPoints`.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
bflatastic
Nigel Ihza Firdausy