Implement Percentage support for gap styles (#1643)

Summary:
X-link: https://github.com/facebook/react-native/pull/44067

X-link: https://github.com/facebook/litho/pull/980

Pull Request resolved: https://github.com/facebook/yoga/pull/1643

Changelog [Internal]:
- Added percentage value for flex layout gap
- Wired up to pass proper available width and height to implement this feature

Reviewed By: NickGerleman

Differential Revision: D56002340

fbshipit-source-id: c0bc86ac70a1391f115c87da99c2ef411535f68b

javascript/src/Node.h

@@ -124,6 +124,7 @@ class Node {
   void setPaddingPercent(int edge, double padding);
 
   void setGap(int gutter, double gapLength);
+  void setGapPercent(int gutter, double gapLength);
 
  public: // Style getters
   int getPositionType(void) const;