Say on_axis for the lift, so it is not indexing's word

`PlaceDescAxis::axis(axis)` shared its name with `PlaceDesc`'s extraction,
which is now `Index<Axis>` and reads `place[axis]`. The two go opposite
directions, so they get different words: `on_axis` pairs with the
`from_axis` it is the shorthand for.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

core/src/ui/place.rs

@@ -50,7 +50,7 @@ impl PlaceDescAxis {
     /// a container dividing one axis says, since nothing divides the other.
     /// [`PlaceDesc::from_axis`] says the across one where it is not the
     /// whole.
-    pub const fn axis(self, axis: Axis) -> PlaceDesc {
+    pub const fn on_axis(self, axis: Axis) -> PlaceDesc {
         PlaceDesc::from_axis(axis, self, Self::WHOLE)
     }