Modify private apis to set, store, and get intrinsic sizing keywords (#1721)

Summary:
Pull Request resolved: https://github.com/facebook/yoga/pull/1721

X-link: https://github.com/facebook/react-native/pull/46938

The private internals of how we store styles needed to change a bit to support 3 new keyword values. Right now the only other keyword that can be stored is `auto`. As a result there isn't much fancy logic to support storing this and its just stored as a specific type inside of `StyleValueHandle`. There are only 3 bits for types (8 values), so it is not sustainable to just stuff every keyword in there. So the change writes the keyword as a value with a new `keyword` `Type`.

I chose not to put `auto` in there even though it is a keyword since it is a hot path, I did not want to regress perf when I did not need to.

I also make a new `StyleSizeValue` class to store size values - so values for `width`, `height`, etc. This way these new keywords are kept specific to sizes and we will not be able to create, for example, a margin: `max-content`.

Changelog: [Internal]

Reviewed By: NickGerleman

Differential Revision: D63927512

fbshipit-source-id: 7285469d37ac4b05226183b56275c77f0c06996c

javascript/src/generated/YGEnums.ts

@@ -125,6 +125,9 @@ export enum Unit {
   Point = 1,
   Percent = 2,
   Auto = 3,
+  MaxContent = 4,
+  FitContent = 5,
+  Stretch = 6,
 }
 
 export enum Wrap {
@@ -203,6 +206,9 @@ const constants = {
   UNIT_POINT: Unit.Point,
   UNIT_PERCENT: Unit.Percent,
   UNIT_AUTO: Unit.Auto,
+  UNIT_MAX_CONTENT: Unit.MaxContent,
+  UNIT_FIT_CONTENT: Unit.FitContent,
+  UNIT_STRETCH: Unit.Stretch,
   WRAP_NO_WRAP: Wrap.NoWrap,
   WRAP_WRAP: Wrap.Wrap,
   WRAP_WRAP_REVERSE: Wrap.WrapReverse,