feat(tazjin/rlox): Implement variable depth resolver

Implements the first part of the resolver from
https://craftinginterpreters.com/resolving-and-binding.html

This is wired up to the execution paths in main, but not yet in the
tests. The resolved depth is also not actually used for variable
lookups (yet).

Change-Id: I3a8615252b7b9b12d5a290c5ddf85988f61b9184
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2403
Reviewed-by: tazjin <mail@tazj.in>
Tested-by: BuildkiteCI

users/tazjin/rlox/src/errors.rs

@@ -14,6 +14,7 @@ pub enum ErrorKind {
     InternalError(String),
     InvalidAssignmentTarget(String),
     RuntimeError(String),
+    StaticError(String),
 
     // This variant is not an error, rather it is used for
     // short-circuiting out of a function body that hits a `return`