Use wp_get_global_settings() instead of private API

Changes the resolver to use wp_get_global_settings() instead of
the chained objects to get the merged data layer.

Reference:
WordPress/gutenberg#53805

Props @oandregal.

src/wp-includes/fonts/font-face/class-wp-font-face-resolver.php

@@ -26,7 +26,7 @@ class WP_Font_Face_Resolver {
 	 * @return array Returns the font-families, each with their font-face variations.
 	 */
 	public static function get_fonts_from_theme_json() {
-		$settings = WP_Theme_JSON_Resolver::get_merged_data()->get_settings();
+		$settings = wp_get_global_settings();
 
 		// Bail out early if there are no font settings.
 		if ( empty( $settings['typography'] ) || empty( $settings['typography']['fontFamilies'] ) ) {