SDK-562 make the plugin method public.

Author: echo-branch

Branch-SDK/Branch-SDK/Branch.h

@@ -690,6 +690,9 @@ typedef NS_ENUM(NSUInteger, BranchCreditHistoryOrder) {
 
 - (void)suppressWarningLogs;
 
+// For use by other Branch SDKs.  For example, Unity or React Native.
+- (void)registerPluginName:(NSString *)name version:(NSString *)version;
+
 /**
  Key-value pairs to be included in the metadata on every request.