Breaking: YGConfigRef related const-correctness fixes (#1371)

Summary:
X-link: https://github.com/facebook/react-native/pull/39374

Pull Request resolved: https://github.com/facebook/yoga/pull/1371

Right now `YGConfigGetDefault` and `YGNodeGetConfig` both return mutable, freeable, configs, which is bad, since the former points to a global singleton config, and the latter usually does too. Mutating this is not thread safe, and it should never be freed.

This change makes these functions return `YGConfigConstRef` to prevent mutation, and also lets us allow `YGConfigNewWithConfig` to accept a const config. If a caller does want to mutate a config (such as to free it), it must be tracked manually.

Changelog: [Internal]

Reviewed By: javache

Differential Revision: D49132476

fbshipit-source-id: ac9ce61149e69c6c25cadb99711435b0a5b9f38a

yoga/node/Node.cpp

@@ -17,7 +17,9 @@
 
 namespace facebook::yoga {
 
-Node::Node(yoga::Config* config) : config_{config} {
+Node::Node() : Node{&Config::getDefault()} {}
+
+Node::Node(const yoga::Config* config) : config_{config} {
   yoga::assertFatal(
       config != nullptr, "Attempting to construct Node with null config");
 
@@ -285,7 +287,7 @@ void Node::setConfig(yoga::Config* config) {
       config->useWebDefaults() == config_->useWebDefaults(),
       "UseWebDefaults may not be changed after constructing a Node");
 
-  if (yoga::configUpdateInvalidatesLayout(config_, config)) {
+  if (yoga::configUpdateInvalidatesLayout(*config_, *config)) {
     markDirtyAndPropagate();
   }