Java model _bits property should be transient

[RicoYao]

The _bits property in the java models should be declared as private transient int _bits so that the _bits property does not get included when a developer serializes a model to JSON.

[rahul-malik]

@RicoYao - Will this prevent it from other serialization methods? For instance if you serialize to disk and read back the same model you'd lose the "is set" capabilities right?

[RicoYao]

@rahul-malik My thinking is that if you read back the model and deserialize it through the generated TypeAdapter, then _bits will be set to the expected value again (because the TypeAdapter uses the Builder which sets _bits).