feat(tazjin/rlox): Support local variables

WIP

Change-Id: I78fbc885faaac165c380cbd9aa98b4b64a9b8274
Reviewed-on: https://cl.tvl.fyi/c/depot/+/3685
Tested-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>

users/tazjin/rlox/src/bytecode/errors.rs

@@ -9,6 +9,7 @@ pub enum ErrorKind {
     ExpectedToken(&'static str),
     InternalError(&'static str),
     TypeError(String),
+    VariableShadowed(String),
 }
 
 #[derive(Debug)]