Add a CLI package #4

I think we should probably have a CLI that wraps over the TypeSpec compiler. Typelex is conceptually its own IDL but I'm too lazy to actually do that and it's nice to reuse the TypeSpec ecosystem. Still, maybe we want to hide some of TypeSpec as implementation details.

I imagine a CLI would do the following:

• Let you bootstrap Typelex pipeline in an existing project with one command.
• Hide the TypeSpec configuration (or at least make it optional). Assume lexicons/ as the output folder.
• Probably encapsulate the knowledge about which TypeSpec version we're compatible with.

This may also be useful for building higher-level features specific to Lexicons.