Interfacing converted models with MIL Builder

## ❓Question

Is it possible to interface models converted to mlprogram with the mil builder? This would help with creating program with control flow without the hurdle of mixing scripted/traced torchscript models

Start with the MIL Builder entry point and the interface used by models converted to mlprogram. Determine whether the two representations can be combined for control flow without mixing scripted and traced TorchScript models. Done should be a clearly scoped supported integration or a documented limitation.

Written by the indexing model from the issue text.