fix(c-api) Fix how wasm_frame_t is implemented.

In `wasm.h`, `wasm_frame_t` is implemented with `WASM_DECLARE_TYPE`,
so with `WASM_DECLARE_VEC(frame, *)`. This `*` means the C struct for
the vector is defined:

```c
struct wasm_frame_vec_t {
    size_t size;
    wasm_frame_t** data;
}
```

The way we implement `wasm_frame_vec_t` in Rust is with the
`wasm_declare_vec!` macro. And it is wrong. We must use
`wasm_declared_boxed_vec!`.

lib/c-api/src/wasm_c_api/types/frame.rs

@@ -48,4 +48,4 @@ pub unsafe extern "C" fn wasm_frame_module_offset(frame: &wasm_frame_t) -> usize
     frame.info.module_offset()
 }
 
-wasm_declare_vec!(frame);
+wasm_declare_boxed_vec!(frame);