Call logger from within YGConfig

Summary:
@public

Stricter encapsulation of logging callbacks within `YGConfig`.

Instead of invoking the logging callback directly (`node->logger(...)`), callers now have to go through `YGConfig::log()`.

This change will allow us to add the concept of a *Layout Context,* where logging functions will be able to receive an additional `void *` argument if configured accordingly. This API will be used internally for Yoga’s JNI bindings, to avoid storing a weak JNI reference for each node, and avoid reference table overflows.

Changed API:

- `YGConfig::logger()` -> `YGConfig::log()`

Reviewed By: SidharthGuglani

Differential Revision: D14123483

fbshipit-source-id: 87b8bb7de0e4346b6a41e57a70ac4eb8d79b24af

yoga/Yoga.cpp

@@ -4182,12 +4182,12 @@ void YGNodeCalculateLayout(
 
 void YGConfigSetLogger(const YGConfigRef config, YGLogger logger) {
   if (logger != nullptr) {
-    config->logger = logger;
+    config->setLogger(logger);
   } else {
 #ifdef ANDROID
-    config->logger = &YGAndroidLog;
+    config->setLogger(&YGAndroidLog);
 #else
-    config->logger = &YGDefaultLog;
+    config->setLogger(&YGDefaultLog);
 #endif
   }
 }