Uncouple Java hasbits from C++ hasbits.

There is really no reason for the Java compiler code to call into the internal
C++ implementation of HasHasbit. In the future, the two implementations may
evolve separately and this decoupling can make it easier.

PiperOrigin-RevId: 686672397

src/google/protobuf/compiler/java/helpers.h

@@ -338,7 +338,7 @@ bool HasRequiredFields(const Descriptor* descriptor);
 bool IsRealOneof(const FieldDescriptor* descriptor);
 
 inline bool HasHasbit(const FieldDescriptor* descriptor) {
-  return internal::cpp::HasHasbit(descriptor);
+  return descriptor->has_presence() && !descriptor->real_containing_oneof();
 }
 
 // Check whether a message has repeated fields.