Move `get_c_interface` into toml files.

[erick-xanadu]

Soon after specifying toml files, we can have a the C interface also defined in the toml file. It makes sense to have all this information in one place.

[dime10]

Does that make sense? I think the reason it was made a function call is so that the device can compute the correct location of the library at runtime.

I suppose knowing where the config file is would be sufficient to then describe a relative path to the shared library in the toml, assuming I'm not missing something 🤔

[erick-xanadu]

I suppose knowing where the config file is would be sufficient to then describe a relative path to the shared library in the toml, assuming I'm not missing something 🤔

Yep!