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

yoga/style/StyleLength.h

@@ -19,13 +19,11 @@ namespace facebook::yoga {
  * 3. A CSS <length-percentage> value:
  *    a. <length> value (e.g. 10px)
  *    b. <percentage> value of a reference <length>
- * 4. (soon) A math function which returns a <length-percentage> value
  *
  * References:
  * 1. https://www.w3.org/TR/css-values-4/#lengths
  * 2. https://www.w3.org/TR/css-values-4/#percentage-value
  * 3. https://www.w3.org/TR/css-values-4/#mixed-percentages
- * 4. https://www.w3.org/TR/css-values-4/#math
  */
 class StyleLength {
  public:
@@ -59,6 +57,14 @@ class StyleLength {
     return unit_ == Unit::Undefined;
   }
 
+  constexpr bool isPoints() const {
+    return unit_ == Unit::Point;
+  }
+
+  constexpr bool isPercent() const {
+    return unit_ == Unit::Percent;
+  }
+
   constexpr bool isDefined() const {
     return !isUndefined();
   }
@@ -67,10 +73,6 @@ class StyleLength {
     return value_;
   }
 
-  constexpr Unit unit() const {
-    return unit_;
-  }
-
   constexpr FloatOptional resolve(float referenceLength) {
     switch (unit_) {
       case Unit::Point:
@@ -90,6 +92,11 @@ class StyleLength {
     return value_ == rhs.value_ && unit_ == rhs.unit_;
   }
 
+  constexpr bool inexactEquals(const StyleLength& other) const {
+    return unit_ == other.unit_ &&
+        facebook::yoga::inexactEquals(value_, other.value_);
+  }
+
  private:
   // We intentionally do not allow direct construction using value and unit, to
   // avoid invalid, or redundant combinations.
@@ -101,7 +108,7 @@ class StyleLength {
 };
 
 inline bool inexactEquals(const StyleLength& a, const StyleLength& b) {
-  return a.unit() == b.unit() && inexactEquals(a.value(), b.value());
+  return a.inexactEquals(b);
 }
 
 } // namespace facebook::yoga