Separate the `headcrab::symbol` module into a crate

[nbaksalyar]

This is a tracking issue.

Reasons for this change:

1. Users might want to use functions related to symbolication outside the context of an interactive debugger (e.g., for eBPF).
2. This change would decouple the symbolication logic from the core debugger functions.
3. It would simplify integration with the Rust compiler API (which can be separated into another optional crate).