feat(c-api) Redefine wasm_store_t.

`wasm_store_t` is now a proper struct (rather than an opaque type) of
kind:

```rs
struct wasm_store_t {
    inner: Store
}
```

The rest of the patch updates the code accordingly.

lib/c-api/src/wasm_c_api/instance.rs

@@ -4,7 +4,6 @@ use super::store::wasm_store_t;
 use super::trap::wasm_trap_t;
 use crate::ordered_resolver::OrderedResolver;
 use std::mem;
-use std::ptr::NonNull;
 use std::sync::Arc;
 use wasmer::{Extern, Instance};
 
@@ -52,7 +51,7 @@ unsafe fn argument_import_iter(
 
 #[no_mangle]
 pub unsafe extern "C" fn wasm_instance_new(
-    store: Option<NonNull<wasm_store_t>>,
+    _store: &wasm_store_t,
     module: &wasm_module_t,
     imports: *const *const wasm_extern_t,
     // own