Backport new WP_Theme_JSON::get_patterns() method.

src/wp-includes/class-wp-theme-json.php

@@ -759,6 +759,21 @@ public function get_template_parts() {
 		return $template_parts;
 	}
 
+	/**
+	 * Returns the current theme's wanted patterns(slugs) to be registered from
+	 * Pattern Directory.
+	 *
+	 * @since 6.0.0
+	 *
+	 * @return array Array of patterns if configured, else empty array.
+	 */
+	public function get_patterns() {
+		if ( isset( $this->theme_json['patterns'] ) && is_array( $this->theme_json['patterns'] ) ) {
+			return $this->theme_json['patterns'];
+		}
+		return array();
+	}
+
 	/**
 	 * Converts each style section into a list of rulesets
 	 * containing the block styles to be appended to the stylesheet.