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

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

```c
struct wasm_tabletype_vec_t {
    size_t size;
    wasm_tabletype_t** data;
}
```

The way we implement `wasm_tabletype_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/table.rs

@@ -53,7 +53,7 @@ impl wasm_tabletype_t {
     }
 }
 
-wasm_declare_vec!(tabletype);
+wasm_declare_boxed_vec!(tabletype);
 
 #[no_mangle]
 pub unsafe extern "C" fn wasm_tabletype_new(