Change default back to position: "relative" (#1469)

Summary:
X-link: https://github.com/facebook/react-native/pull/41480

Pull Request resolved: https://github.com/facebook/yoga/pull/1469

The previous version of static didn't do anything inside of Yoga. Now that we're making it do something, this changes the default back to relative so that users with no errata set don't see their deafult styles changing.

Reviewed By: joevilches

Differential Revision: D51182955

fbshipit-source-id: c0ea357694e1367fb6786f1907dfff784b19a4bc

gentest/gentest.js

@@ -165,7 +165,7 @@ function checkDefaultValues() {
     {style: 'justify-content', value: 'flex-start'},
     {style: 'align-content', value: 'flex-start'},
     {style: 'align-items', value: 'stretch'},
-    {style: 'position', value: 'static'},
+    {style: 'position', value: 'relative'},
     {style: 'flex-wrap', value: 'nowrap'},
     {style: 'overflow', value: 'visible'},
     {style: 'flex-grow', value: '0'},
@@ -643,7 +643,7 @@ function isDefaultStyleValue(style, value) {
   if (defaultStyle == null) {
     switch (style) {
       case 'position':
-        defaultStyle = new Set(['static']);
+        defaultStyle = new Set(['relative']);
         break;
 
       case 'left':