feat(tazjin/rlox): Implement block parsing

Change-Id: I1b7235ed71fa36120984a36f22cd564f59581352
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2303
Reviewed-by: tazjin <mail@tazj.in>
Tested-by: BuildkiteCI

users/tazjin/rlox/src/errors.rs

@@ -5,6 +5,7 @@ pub enum ErrorKind {
     UnmatchedParens,
     ExpectedExpression(String),
     ExpectedSemicolon,
+    ExpectedClosingBrace,
     ExpectedVariableName,
     TypeError(String),
     UndefinedVariable(String),