gentest support for position: static + initial test

Summary:
I am about to embark on supporting `position: static` in Yoga. The enum exists already (and is the default position type, lol) but does not actually do anything and just behaves like `position: relative`.

My approach here is to write a bunch of tests to test for the various behaviors of static positions and then develop on Yoga afterwards to get those tests passing. To do this, we need to make a few changes to the gentest files as there is not support for adding `position: static` at the moment:

* Make it so that the gentest code can physically write `YGPositionTypeStatic` if it encounters `position: static` in the style
* Make it so that gentest.js knows that Yoga's default is actually static. This way the code generated in the tests will actually label nodes for non default values
* Explicitly label the position type even when it is not declared in the style prop (with the exception of the default)
* Regenerate all the tests

Additionally I added the first, basic test: making sure insets do nothing on a statically positioned element.

Reviewed By: NickGerleman

Differential Revision: D50437855

fbshipit-source-id: 0e8bbf1c224d477ea4592b7563d0b70d2ffa79c8

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: 'relative'},
+    {style: 'position', value: 'static'},
     {style: 'flex-wrap', value: 'nowrap'},
     {style: 'overflow', value: 'visible'},
     {style: 'flex-grow', value: '0'},
@@ -198,8 +198,7 @@ function setupTestTree(
     // Skip position info for root as it messes up tests
     if (
       node.declaredStyle[style] === '' &&
-      (style == 'position' ||
-        style == 'left' ||
+      (style == 'left' ||
         style == 'top' ||
         style == 'right' ||
         style == 'bottom' ||
@@ -576,6 +575,8 @@ function positionValue(e, value) {
   switch (value) {
     case 'absolute':
       return e.YGPositionTypeAbsolute;
+    case 'static':
+      return e.YGPositionTypeStatic;
     default:
       return e.YGPositionTypeRelative;
   }
@@ -642,7 +643,7 @@ function isDefaultStyleValue(style, value) {
   if (defaultStyle == null) {
     switch (style) {
       case 'position':
-        defaultStyle = new Set(['relative']);
+        defaultStyle = new Set(['static']);
         break;
 
       case 'left':