iris: separate layout allocation from lengths

src/widget/layout/max_size.rs

@@ -2,12 +2,12 @@ use crate::prelude::*;
 
 pub struct MaxSize {
     pub inner: StrongWidget,
-    pub x: Option<Len>,
-    pub y: Option<Len>,
+    pub x: Option<LayoutLen>,
+    pub y: Option<LayoutLen>,
 }
 
 impl MaxSize {
-    fn clamp(len: Len, max: Option<Len>, output: f32, density: f32) -> Len {
+    fn clamp(len: LayoutLen, max: Option<LayoutLen>, output: f32, density: f32) -> LayoutLen {
         let Some(max) = max else {
             return len;
         };
@@ -20,7 +20,7 @@ impl MaxSize {
         }
     }
 
-    fn clamp_region(offered_px: f32, max: Option<Len>, output: f32, density: f32) -> UiSpan {
+    fn clamp_region(offered_px: f32, max: Option<LayoutLen>, output: f32, density: f32) -> UiSpan {
         let Some(max) = max else {
             return UiSpan::FULL;
         };