Export YGInteropSetLogger method (#960)

Summary:
When building and using C # libraries,
EntryPointNotFoundException thrown from YGInteropSetLogger.

so, I added YOGA_EXPORT on YGInteropSetLogger.

Pull Request resolved: https://github.com/facebook/yoga/pull/960

Reviewed By: yungsters

Differential Revision: D40027238

Pulled By: yungsters

fbshipit-source-id: 6af584a16e66a31c91374a1bb64434888762e3c8

yoga/Yoga.cpp

@@ -4336,6 +4336,11 @@ YOGA_EXPORT void YGConfigSetUseWebDefaults(
   config->useWebDefaults = enabled;
 }
 
+YOGA_EXPORT bool YGConfigGetUseLegacyStretchBehaviour(
+    const YGConfigRef config) {
+  return config->useLegacyStretchBehaviour;
+}
+
 YOGA_EXPORT void YGConfigSetUseLegacyStretchBehaviour(
     const YGConfigRef config,
     const bool useLegacyStretchBehaviour) {