[EH] Test StackIR's local2stack on translator output (#6264)

This adds `STACKIR-OPT` filecheck lines to `translate-to-new-eh.wast`
to see if StackIR's `local2stack` optimization successfully removes some
of unnecessary `local.set`/`local.get`s.

While supporting the whole Binayren optimization pipeline for the new EH
instructions is not the goal for the very near-term future, StackIR's
`local2stack` optimization can help with a very common pattern generated
by this translator, which is:
```wast
(try $l
  (do ... )
  (catch_all
    (call $destructor)
    (rethrow $l)
  )
)
```
is translated to
```wast
(block $outer
  (local.set $exn     ;; can be optimized away
    (block $catch_all (result exnref)
      (try_table (catch_all_ref $catch_all)
        ...
      )
      (br $outer)
    )
  )
  (call $destructor)
  (throw_ref
    (local.get $exn)  ;; can be optimized away
  )
)
```

Here we don't really need `local.set $exn` and `local.get $exn`, and
these can be optimized away using StackIR's local2stack. After
optimizing them away in Stack IR, the code can be like
```wast
block $outer
  block $catch_all (result exnref)
    try_table (catch_all_ref $catch_all)
      ...
    end
    br $outer
  end
  call $destructor
  throw_ref
end
```

This optimization alone reduces the code size increased caused by
translating significantly. For Adobe Photoshop, the code size increase
goes down from 4.2% to 2.8%, and for Binaryen, it goes down from 3.8% to
2.0%.

Author: aheejin