Reference support for kernel launch arguments

• To capture the argument lifetime of kernel launch (for !88 (merged)), we cannot use pointer because it drop lifetime information

• This MR add a support for reference to kernel definitions, e.g.

  #[kernel]
  fn f(a: &i32, b: &mut i32) { ... }

• Drop ArgRef trait and ArgRefN structs introduced in !87 (merged), and introduce specialized LaunchableN traits

  • It can capture only immutable reference &'arg T. We need to also capture &'arg mut T
  • We may extend ArgRefN like

    struct ArgRef101<T1, T2, T3> {
      arg1: &'arg mut T1,
      arg2: &'arg T2,
      arg3: &'arg mut T3,
    }

    (1: mutable, 0: immutable) but it needs 2^N variations.
  • I revert it to use tuple as before !87 (merged), and specialize Launchable trait into LaunchableN traits instead