[Wasm-GC] Fix JS API casts for some top types

[Asumu Takikawa]

There are a small number of cases in the JS API cast code that makes too-optimistic assumptions for top types (because the code was originally written to implement cast instructions, which benefit from static type-checking). Example diff for js-api.js: 

```
+  {
+    let m1 = instantiate(`
+      (module
+        (func (export "f"))
+      )
+    `);
+    assert.throws(
+      () => instantiate(`
+        (module
+          (global (import "m" "f") (ref any))
+        )
+      `, { m: { f: m1.exports.f } }),
+      WebAssembly.LinkError,
+      "Argument value did not match the reference type"
+    )
+  }
```

There's a simple fix for these cases.

[Asumu Takikawa]

Pull request: https://github.com/WebKit/WebKit/pull/25599

[Radar WebKit Bug Importer]

<rdar://problem/124294503>

[EWS]

Committed 276580@main (a2bcc4921f7c): <https://commits.webkit.org/276580@main>

Reviewed commits have been landed. Closing PR #25599 and removing active labels.