Rename a length's abs component to px

`dp` is coming, and then `abs` says which of the two it is not. The
component has always been a pixel count, so the name that admits it is
the one that leaves room for a second unit beside it.

Mechanical: the field on `Len` and `UiScalar`, their constructors,
`to_abs`/`get_abs`, the matching WGSL struct member and the locals
composing it. Field order and types are unchanged, so the `Pod` layout
the shader reads is the same bytes. `f32::abs` is untouched.

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

core/src/orientation/len.rs

@@ -9,14 +9,14 @@ pub struct Size {
 
 #[derive(Debug, Clone, Copy, PartialEq)]
 pub struct Len {
-    pub abs: f32,
+    pub px: f32,
     pub rel: f32,
     pub rest: f32,
 }
 
 impl<N: UiNum> From<N> for Len {
     fn from(value: N) -> Self {
-        Len::abs(value.to_f32())
+        Len::px(value.to_f32())
     }
 }
 
@@ -46,10 +46,10 @@ impl Size {
         y: Len::REST,
     };
 
-    pub fn abs(v: Vec2) -> Self {
+    pub fn px(v: Vec2) -> Self {
         Self {
-            x: Len::abs(v.x),
-            y: Len::abs(v.y),
+            x: Len::px(v.x),
+            y: Len::px(v.y),
         }
     }
 
@@ -97,13 +97,13 @@ impl Size {
 
 impl Len {
     pub const ZERO: Self = Self {
-        abs: 0.0,
+        px: 0.0,
         rel: 0.0,
         rest: 0.0,
     };
 
     pub const REST: Self = Self {
-        abs: 0.0,
+        px: 0.0,
         rel: 0.0,
         rest: 1.0,
     };
@@ -111,27 +111,27 @@ impl Len {
     pub fn apply_rest(&self) -> UiScalar {
         UiScalar {
             rel: self.rel + if self.rest > 0.0 { 1.0 } else { 0.0 },
-            abs: self.abs,
+            px: self.px,
         }
     }
 
-    pub fn abs(abs: impl UiNum) -> Self {
+    pub fn px(px: impl UiNum) -> Self {
         Self {
-            abs: abs.to_f32(),
+            px: px.to_f32(),
             rel: 0.0,
             rest: 0.0,
         }
     }
     pub fn rel(rel: impl UiNum) -> Self {
         Self {
-            abs: 0.0,
+            px: 0.0,
             rel: rel.to_f32(),
             rest: 0.0,
         }
     }
     pub fn rest(ratio: impl UiNum) -> Self {
         Self {
-            abs: 0.0,
+            px: 0.0,
             rel: 0.0,
             rest: ratio.to_f32(),
         }
@@ -141,31 +141,31 @@ impl Len {
 pub mod len_fns {
     use super::*;
 
-    pub fn abs(abs: impl UiNum) -> Len {
+    pub fn px(px: impl UiNum) -> Len {
         Len {
-            abs: abs.to_f32(),
+            px: px.to_f32(),
             rel: 0.0,
             rest: 0.0,
         }
     }
     pub fn rel(rel: impl UiNum) -> Len {
         Len {
-            abs: 0.0,
+            px: 0.0,
             rel: rel.to_f32(),
             rest: 0.0,
         }
     }
     pub fn rest(ratio: impl UiNum) -> Len {
         Len {
-            abs: 0.0,
+            px: 0.0,
             rel: 0.0,
             rest: ratio.to_f32(),
         }
     }
 }
 
-impl_op!(Len Add add; abs rel rest);
-impl_op!(Len Sub sub; abs rel rest);
+impl_op!(Len Add add; px rel rest);
+impl_op!(Len Sub sub; px rel rest);
 
 impl_op!(Size Add add; x y);
 impl_op!(Size Sub sub; x y);
@@ -184,8 +184,8 @@ impl std::fmt::Display for Size {
 
 impl std::fmt::Display for Len {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        if self.abs != 0.0 {
-            write!(f, "{} abs;", self.abs)?;
+        if self.px != 0.0 {
+            write!(f, "{} px;", self.px)?;
         }
         if self.rel != 0.0 {
             write!(f, "{} rel;", self.rel)?;