export ToasterProps type (#400)

For Sonner to be bundled in other libraries, we need to export `ToasterProps`.

This fixes following error for library authors:
```
TS4023: Exported variable 'X' has or is using name 'ToasterProps' from external module './node_modules/sonner/dist/index' but cannot be named
```

src/index.tsx

@@ -722,4 +722,4 @@ const Toaster = (props: ToasterProps) => {
  </section>
  );
 };
-export { toast, Toaster, type ExternalToast, type ToastT };
+export { toast, Toaster, type ExternalToast, type ToastT, type ToasterProps };