Migrate syntax reflection to new feature-based system.

PiperOrigin-RevId: 516641207

Author: mkruskal-google

protobuf/compiler/src/google/protobuf/compiler/j2objc/j2objc_field.cc

@@ -283,8 +283,7 @@ void FieldGenerator::GenerateStaticRefs(io::Printer *printer) const {
 SingleFieldGenerator::SingleFieldGenerator(
     const FieldDescriptor *descriptor, uint32_t *numHasBits)
   : FieldGenerator(descriptor) {
-  if (descriptor->containing_oneof() == nullptr ||
-      descriptor->containing_oneof()->is_synthetic()) {
+  if (descriptor->real_containing_oneof() == nullptr) {
     variables_["has_bit_index"] = SimpleItoa((*numHasBits)++);
   }
 }

protobuf/compiler/src/google/protobuf/compiler/j2objc/j2objc_message.cc

@@ -377,7 +377,7 @@ void MessageGenerator::GenerateSource(io::Printer* printer) {
   }
   for (int i = 0; i < descriptor_->oneof_decl_count(); i++) {
     const OneofDescriptor* oneof = descriptor_->oneof_decl(i);
-    if (oneof->is_synthetic()) {
+    if (oneof->field_count() == 1) {
       field_generators_.get(oneof->field(0)).GenerateDeclaration(printer);
     } else {
       printer->Print("union {\n");