bevy_ui::layout::round_ties_up

* Added comments explaining the behaviour of the `round_ties_up` function.
* Changed the first predicate to use `<=` instead of `<`. This doesn't change the function's behaviour (since `(0.).ceil() == 0.`) but it feels like it makes it a little easier to undertand.

crates/bevy_ui/src/layout/mod.rs

@@ -368,9 +368,12 @@ pub fn ui_layout_system(
 #[inline]
 /// Round `value` to the closest whole integer, with ties (values with a fractional part equal to 0.5) rounded towards positive infinity.
 fn round_ties_up(value: f32) -> f32 {
-    if 0. < value || value.fract() != 0.5 {
+    if 0. <= value || value.fract() != 0.5 {
+        // The `round` function rounds ties away from zero. For positive numbers "away from zero" is towards positive infinity.
+        // So for all positive values, and negative values with a fractional part not equal to 0.5, `round` returns the correct result.
         value.round()
     } else {
+        // In the remaining cases, where `value` is negative and its fractional part is equal to 0.5, we use `ceil` to round it up towards positive infinity.
         value.ceil()
     }
 }