Splay bends away from the centre of the layer's bounds, as the reference
tool's does: on a ring or an L that centre lies outside the shape, so an
inner edge bends towards the hole. Checked side by side on a ring and an
L at Splay 0% and 100%. The module doc still said splay 0 bends along the
edge's normal; it bends towards the core since #1889.
`MAX_SHAPE_PX` now says it is 4M px on the desktop and 1M on the web, and
that a bigger shape gets no core, so a large glass text or vector can bend
differently once zoomed into, in a 2× export, or on the web.
Docs only.