ReCAPTCHA3 should use WP HTTP API

The reCAPTCHA3 addon currently uses file_get_contents to query the Google API. This requires the PHP setting allow_url_fopen to be enabled, which is not always the case and might not be configurable by users of this plugin.

Instead, the plugin should use the WordPress HTTP API to make the request i.e. with wp_remote_get https://developer.ww.wp.xz.cn/plugins/http-api/#getting-data-from-an-api