Support "align-content: space-evenly" (#1422)

Summary:
X-link: https://github.com/facebook/react-native/pull/41019

### Changes made
- Regenerated tests (as some aspect ratio tests seem to be out of date compared to the fixtures)
- Added SpaceEvenly variant to the "Align" enums (via enums.py)
- Implemented `align-content: space-evenly` alignment in CalculateLayout.cpp
- Added generated tests `align-content: space-evenly`
- Updated NumericBitfield test to account for the fact that the Align enum now requires more bits (this bit could do with being reviewed as I am not 100% certain that it's valid to just update the test like this).

### Changes not made
- Any attempt to improve the spec-compliance of content alignment in general (e.g. I think https://github.com/facebook/yoga/pull/1013 probably still needs to happen)

Pull Request resolved: https://github.com/facebook/yoga/pull/1422

Reviewed By: yungsters

Differential Revision: D50305438

Pulled By: NickGerleman

fbshipit-source-id: ef9f6f14220a0db066bc30db8dd690a4a82a0b00

java/com/facebook/yoga/YogaAlign.java

@@ -17,7 +17,8 @@ public enum YogaAlign {
   STRETCH(4),
   BASELINE(5),
   SPACE_BETWEEN(6),
-  SPACE_AROUND(7);
+  SPACE_AROUND(7),
+  SPACE_EVENLY(8);
 
   private final int mIntValue;
 
@@ -39,6 +40,7 @@ public enum YogaAlign {
       case 5: return BASELINE;
       case 6: return SPACE_BETWEEN;
       case 7: return SPACE_AROUND;
+      case 8: return SPACE_EVENLY;
       default: throw new IllegalArgumentException("Unknown enum value: " + value);
     }
   }