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- Regenerated tests (as some aspect ratio tests seem to be out of date compared to the fixtures)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

javascript/src/generated/YGEnums.ts

@@ -16,6 +16,7 @@ export enum Align {
   Baseline = 5,
   SpaceBetween = 6,
   SpaceAround = 7,
+  SpaceEvenly = 8,
 }
 
 export enum Dimension {
@@ -141,6 +142,7 @@ const constants = {
   ALIGN_BASELINE: Align.Baseline,
   ALIGN_SPACE_BETWEEN: Align.SpaceBetween,
   ALIGN_SPACE_AROUND: Align.SpaceAround,
+  ALIGN_SPACE_EVENLY: Align.SpaceEvenly,
   DIMENSION_WIDTH: Dimension.Width,
   DIMENSION_HEIGHT: Dimension.Height,
   DIRECTION_INHERIT: Direction.Inherit,