pub fn layout(
size: impl Fn(&Subviews<'_>, Proposal) -> (f64, f64) + Send + Sync + 'static,
place: impl Fn(&Subviews<'_>, Rect, Proposal) + Send + Sync + 'static,
) -> CustomLayoutExpand description
Build a layout from a sizing pass and a placement pass.
For a layout with parameters, implement views::LayoutAlgorithm on a
type and hand it to views::register instead.