Bug 243265

A test case like the following will currently raise an assertion error:

```
//@ runWebAssemblySuite("--useWebAssemblyTypedFunctionReferences=true", "--useWebAssemblyGC=false")

import * as assert from "../assert.js";
import { compile, instantiate } from "./wast-wrapper.js";

let m1 = instantiate(`
  (module
    (type (func))
    (type (func (result (ref 0))))
    (elem declare funcref (ref.func 0))
    (func)
    (func (export "f") (type 1) (ref.func 0))
  )
`);

instantiate(`
  (module
    (type (func))
    (type (func (result (ref 0))))
    (func (import "m" "f") (type 1))
  )
`, { m: { f: m1.exports.f } });
```

This will instead raise a parse error if typed funcrefs are turned off (the default).

The assertion failure comes from a ref-with-index type not being supported in `WasmToJS.cpp` in processing the result of an exported Wasm function. I think it should be possible to support this case, it just requires checking if the type index points to a function signature or not. For non-function signatures, it should probably error for now.