How to access google.protobuf.FieldOptions extensions?

[bowenjin]

Is there a way to read the FieldOption extension values for some proto field?

Say for FieldBehavior https://github.com/googleapis/googleapis/blob/master/google/api/field_behavior.proto

If I have a proto such as

message Message{
  string text = 1 [
      (google.api.field_behavior) = REQUIRED
  ];
}

That gets generated to dart, how can I read the FieldOption value on the text field?