message: When printing bytecode use amp for local
  Summary: Use `&` as prefix for local slots ids. Previously `l` was used, which was not very readable.
diff: @@ -291,7 +291,7 @@ impl<T: StarlarkValue<'static>> BcInstrArg for FrozenValueTyped<'static, T> {
  impl BcInstrArg for LocalSlotId {
  fn fmt_append(param: &Self, _ip: BcAddr, f: &mut dyn Write) -> fmt::Result {
  - write!(f, " l{}", param.0)
  + write!(f, " &{}", param.0)
  }
  fn pops_stack(_: &Self) -> u32 {
  