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.cpp

@@ -240,6 +240,10 @@ void Node::setGap(int gutter, double gapLength) {
   YGNodeStyleSetGap(m_node, static_cast<YGGutter>(gutter), gapLength);
 }
 
+void Node::setGapPercent(int gutter, double gapLength) {
+  YGNodeStyleSetGapPercent(m_node, static_cast<YGGutter>(gutter), gapLength);
+}
+
 int Node::getPositionType(void) const {
   return YGNodeStyleGetPositionType(m_node);
 }