Fix LocalCSE's usable local selection (#2638)

Now that we have subtypes, we cannot reuse any local that contains the
same expression, because that local's type can be a supertype. For
example:
```
(local $0 anyref)
(local $1 nullref)
...
(local.set $0 (ref.null))
(local.set $1 (ref.null)) ;; cannot be replaced with (local.get $0)
```

This extends `usables` map's key to contain both `HashedExpression` and
the local's type, so we can get the right usable local in presence of
subtypes.

0 files changed, 0 insertions, 0 deletions