Add back GeneratedClassName to public (#4686)

These methods are used by grpc

src/google/protobuf/compiler/php/php_generator.h

@@ -49,6 +49,16 @@ class LIBPROTOC_EXPORT Generator
       GeneratorContext* generator_context,
       string* error) const;
 
+  // To skip reserved keywords in php, some generated classname are prefixed.
+  // Other code generators may need following API to figure out the actual
+  // classname.
+  LIBPROTOC_EXPORT std::string GeneratedClassName(
+      const google::protobuf::Descriptor* desc);
+  LIBPROTOC_EXPORT std::string GeneratedClassName(
+      const google::protobuf::EnumDescriptor* desc);
+  LIBPROTOC_EXPORT std::string GeneratedClassName(
+      const google::protobuf::ServiceDescriptor* desc);
+
 };
 
 }  // namespace php