Implement communication layer between cadl emitter and language specific process

[timotheeguerin]

Provide a way for the intermediate codemodel to be sent to the language specific process.

This is not the IPC Layer, this is to work with the current intermediate model where we have hybrid typescript and language sepcific logic.

Options for implementing this:

1. Write file to disk, start external process passing the file to it autorest-python --cadl-codemodel=/tmp/cadlcodemode.yaml
2. Start RPC process similar to autorest and send file via rpc

[markcowl]

estimate: 5