Allow to use JNI without global refs

Summary:
@public

Adds the ability to opt into avoiding global weak JNI refs via `YogaConfig`.

Note that only homogeneous trees are supported, i.e. **mixing weak-ref and non-weak-ref nodes will break!**

Not using JNI refs hopefully will help with avoiding JNI reference table overflows, and will help creating trees on multiple threads, as no lock has to be acquired at any time.

Reviewed By: SidharthGuglani

Differential Revision: D14151037

fbshipit-source-id: 56d94713d39aee080d54be4cb4cdf5e3eccb473a

yoga/YGConfig.h

@@ -10,7 +10,7 @@
 #include "Yoga.h"
 
 struct YGConfig {
-  using LogWithContextFn = void (*)(
+  using LogWithContextFn = int (*)(
       YGConfigRef config,
       YGNodeRef node,
       YGLogLevel level,