Compare regions, not four loose numbers

`PixelRegion` derives `PartialEq`, `Clone` and `Copy`, so `assert_corners!`
compares one against another instead of flattening both to a tuple whose
order there was nothing to check. A failure now prints two regions.

core/src/orientation/pos.rs

@@ -421,7 +421,7 @@ impl Display for UiRegion {
     }
 }
 
-#[derive(Debug)]
+#[derive(Debug, Clone, Copy, PartialEq)]
 pub struct PixelRegion {
     pub top_left: Vec2,
     pub bot_right: Vec2,

src/harness.rs

@@ -22,22 +22,18 @@ impl TaskQueue<DefaultRsc<HarnessState>> for Queue {
     }
 }
 
-/// `assert_eq!` for where a frame put a widget, which `PixelRegion` cannot do
-/// for itself: it neither compares nor prints.
+/// `assert_eq!` for where a frame put a widget, written as its two corners.
 #[macro_export]
 macro_rules! assert_corners {
-    ($harness:expr, $id:expr, ($x0:expr, $y0:expr), ($x1:expr, $y1:expr)) => {{
-        let region = $harness.region(&$id).expect("widget drew nothing");
+    ($harness:expr, $id:expr, ($x0:expr, $y0:expr), ($x1:expr, $y1:expr)) => {
         assert_eq!(
-            (
-                region.top_left.x,
-                region.top_left.y,
-                region.bot_right.x,
-                region.bot_right.y
-            ),
-            ($x0 as f32, $y0 as f32, $x1 as f32, $y1 as f32)
+            $harness.region(&$id).expect("widget drew nothing"),
+            $crate::core::PixelRegion {
+                top_left: $crate::core::util::Vec2::new($x0 as f32, $y0 as f32),
+                bot_right: $crate::core::util::Vec2::new($x1 as f32, $y1 as f32),
+            }
         );
-    }};
+    };
 }
 pub use crate::assert_corners;