Fix flooring of border (#1562)

Summary:
X-link: https://github.com/facebook/react-native/pull/42411

Pull Request resolved: https://github.com/facebook/yoga/pull/1562

I added a small regression D52605596, where negative border would not be correctly floored. This fixes that, and starts adding tests specifically targeting the computed style API, now decoupled from the yoga node.

Reviewed By: joevilches

Differential Revision: D52930827

fbshipit-source-id: e165dade705a8de54c92d65f3664c9081137788c

yoga/style/Style.h

@@ -312,28 +312,32 @@ class YG_EXPORT Style {
   }
 
   float computeFlexStartBorder(FlexDirection axis, Direction direction) const {
-    return computeBorder(flexStartEdge(axis), direction)
-        .resolve(0.0f)
-        .unwrapOrDefault(0.0f);
+    return maxOrDefined(
+        computeBorder(flexStartEdge(axis), direction).resolve(0.0f).unwrap(),
+        0.0f);
   }
 
   float computeInlineStartBorder(FlexDirection axis, Direction direction)
       const {
-    return computeBorder(inlineStartEdge(axis, direction), direction)
-        .resolve(0.0f)
-        .unwrapOrDefault(0.0f);
+    return maxOrDefined(
+        computeBorder(inlineStartEdge(axis, direction), direction)
+            .resolve(0.0f)
+            .unwrap(),
+        0.0f);
   }
 
   float computeFlexEndBorder(FlexDirection axis, Direction direction) const {
-    return computeBorder(flexEndEdge(axis), direction)
-        .resolve(0.0f)
-        .unwrapOrDefault(0.0f);
+    return maxOrDefined(
+        computeBorder(flexEndEdge(axis), direction).resolve(0.0f).unwrap(),
+        0.0f);
   }
 
   float computeInlineEndBorder(FlexDirection axis, Direction direction) const {
-    return computeBorder(inlineEndEdge(axis, direction), direction)
-        .resolve(0.0f)
-        .unwrapOrDefault(0.0f);
+    return maxOrDefined(
+        computeBorder(inlineEndEdge(axis, direction), direction)
+            .resolve(0.0f)
+            .unwrap(),
+        0.0f);
   }
 
   float computeFlexStartPadding(