Fix issue where we were not applying flex end correctly when justifying (#1487)

Summary:
Pull Request resolved: https://github.com/facebook/yoga/pull/1487

X-link: https://github.com/facebook/react-native/pull/41691

The code here was just wrong. I changed it to be the same logic as the Justify:FlexStart case, but with the flex end sides. Then I get the position for the opposite edge since we need to write to flex start side.

Reviewed By: NickGerleman

Differential Revision: D51383792

fbshipit-source-id: 372835a44edff361dbd84dd92ff9f2ec844b9f9c

yoga/algorithm/AbsoluteLayout.cpp

@@ -31,8 +31,14 @@ static void justifyAbsoluteChild(
       break;
     case Justify::FlexEnd:
       child->setLayoutPosition(
-          (parent->getLayout().measuredDimension(dimension(mainAxis)) -
-           child->getLayout().measuredDimension(dimension(mainAxis))),
+          getPositionOfOppositeEdge(
+              parent->getLayout().border(flexEndEdge(mainAxis)) +
+                  parent->getLayout().padding(flexEndEdge(mainAxis)) +
+                  child->getFlexEndMargin(
+                      mainAxis, direction, containingBlockWidth),
+              mainAxis,
+              parent,
+              child),
           flexStartEdge(mainAxis));
       break;
     case Justify::Center: