Structured Interface Definitions In JSON Output

It would be helpful for tools that are consuming the JSON output to have a more structured representation of the interface in the act spec (i.e. function name, number of args, types of args, arg names). Right now we just output a single string and it's not really nice to consume.

Ideally the output would have the same format as that output by solc in the output json, since many tools already know how to consume this format.

Start by locating the act spec JSON output and the code that currently serializes each interface as a single string. Compare its output with the solc output JSON format, including function names, argument counts, types, and names. Done means consumers receive structured interface definitions compatible with that format.

Written by the indexing model from the issue text.