style: Use NonNegative more in the border code.

This ended up not being so small of a patch as I'd have thought, since it
propagated a bit. But most of it is mechanical. Interesting part is
NonNegativeNumberOrPercentage and the actual uses of the NonNegative stuff and
during parsing.

This looks like it'd fix a few correctness issues during interpolation for all
the types except for BorderRadius and co (which handled it manually).

I should write tests for those in a different patch.

Differential Revision: https://phabricator.services.mozilla.com/D14673

components/style/values/generics/border.rs

@@ -45,6 +45,8 @@ pub struct BorderImageSlice<NumberOrPercentage> {
     MallocSizeOf,
     PartialEq,
     SpecifiedValueInfo,
+    ToAnimatedValue,
+    ToAnimatedZero,
     ToComputedValue,
     ToCss,
 )]
@@ -106,19 +108,6 @@ pub struct BorderRadius<LengthOrPercentage> {
     pub bottom_left: BorderCornerRadius<LengthOrPercentage>,
 }
 
-impl<N> From<N> for BorderImageSlice<N>
-where
-    N: Clone,
-{
-    #[inline]
-    fn from(value: N) -> Self {
-        Self {
-            offsets: Rect::all(value),
-            fill: false,
-        }
-    }
-}
-
 impl<L> BorderRadius<L> {
     /// Returns a new `BorderRadius<L>`.
     #[inline]