Add support for `$data` object in `wp_get_plugin_action_button()`

[costdev]

This PR adds support for a $data argument of type object for wp_get_plugin_action_button() as documented.

• Casts $data to object.
  • Some areas of Core use an array, and API calls can return an array or an object.
  • This makes for a cleaner pass-through to install_plugin_install_status().
• Changes references to $data['slug'] to $data->slug instead.