Global Styles: Add support for heading elements (#41981)

* Global Styles: Add support for heading elements

* Collect element style nodes in the order they're defined in ELEMENTS and not in theme.json

Co-authored-by: Adam Zieliński <adam@adamziel.com>

Author: scruffian

lib/compat/wordpress-6.1/class-wp-theme-json-6-1.php

@@ -32,6 +32,7 @@ class WP_Theme_JSON_6_1 extends WP_Theme_JSON_6_0 {
 	 */
 	const ELEMENTS = array(
 		'link'    => 'a:not(.wp-element-button)',
+		'heading' => 'h1, h2, h3, h4, h5, h6',
 		'h1'      => 'h1',
 		'h2'      => 'h2',
 		'h3'      => 'h3',
@@ -342,8 +343,10 @@ protected static function get_style_nodes( $theme_json, $selectors = array() ) {
 		);
 
 		if ( isset( $theme_json['styles']['elements'] ) ) {
-
-			foreach ( $theme_json['styles']['elements'] as $element => $node ) {
+			foreach ( self::ELEMENTS as $element => $selector ) {
+				if ( ! isset( $theme_json['styles']['elements'][ $element ] ) ) {
+					continue;
+				}
 
 				// Handle element defaults.
 				$nodes[] = array(