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- Regenerated tests (as some aspect ratio tests seem to be out of date compared to the fixtures)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

tests/NumericBitfieldTest.cpp

@@ -191,8 +191,8 @@ TEST(NumericBitfield, third_enum_can_be_set) {
 TEST(NumericBitfield, setting_values_does_not_spill_over) {
   uint32_t flags = 0;
   static constexpr size_t alignOffset = 0;
-  static constexpr size_t edgesOffset = 3;
-  static constexpr size_t boolOffset = 7;
+  static constexpr size_t edgesOffset = 4;
+  static constexpr size_t boolOffset = 8;
 
   uint32_t edge = 0xffffff;
   setEnumData<YGEdge>(flags, edgesOffset, (YGEdge)edge);