feat(tazjin/rlox): Global variable assignment

Needed for example code compatibility.

Change-Id: Id83210eaaad7dcfef5aa238dd3a7ec159f6935e9
Reviewed-on: https://cl.tvl.fyi/c/depot/+/3684
Tested-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>

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

@@ -33,4 +33,5 @@ pub enum OpCode {
     // Variable management
     OpDefineGlobal(usize),
     OpGetGlobal(usize),
+    OpSetGlobal(usize),
 }