Adds protobuf serialization for LibLinear models

[Craigacp]

Description

Adds protobuf serialization for liblinear models. Unfortunately rebuilding a LibLinear Model requires reflective access into the model as the fields are all package private with no setters, so we resort to using a ByteArrayOutputStream to serialize the model using Java serialization before packing it into a protobuf. The protobufs do exist for doing it with reflection, but it'll cause issues with the module system so it's not turned on.

Motivation

We need to move Tribuo off Java serialization.

[pogren]

straightforward protobuf serialization has good test code coverage. I don't understand the purpose of the new methods in LibLinearModel: serializeModel, deserializeModels, and setField which have zero references and zero test code coverage.