Enable specifying list type in computed fields

As far as I can tell, it isn't possible to specify the `of` type of lists in computed fields the way that you can in non-computed fields. Thus, this is possible:

```typescript
fields: {
tags: {
type: "list",
of: { type: "string" },
default: []
}
}
```

But this is not:

```typescript
computedFields: {
segments: {
type: "list",
of: { type: "string" },
resolve: (doc) => { ... }
}
}
```

Instead, you can only specify an untyped list, and in the generated output you end up with this:

```typescript
segments: list
```

But this raw `list` type isn't defined!

There may be reasons to explicitly disallow typed lists in computed fields, and if so I'd be curious why! Otherwise, this feels like an oversight to me.