Toolbar: Load toolbar in `wp_body_open` when available.

For accessibility, the visual appearance and source order should match. Moving the toolbar to load in the new hook `wp_body_open` (5.2) fixes a long-standing source order problem.

Props jankimoradiya, afercia, SergeyBiryukov, audrasjb, ocean90, xkon, dinhtungdu.
Fixes #47053.

Built from https://develop.svn.wordpress.org/trunk@47221


git-svn-id: http://core.svn.wordpress.org/trunk@47021 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/default-filters.php

@@ -537,7 +537,7 @@ add_action( 'template_redirect', '_wp_admin_bar_init', 0 );
 add_action( 'admin_init', '_wp_admin_bar_init' );
 add_action( 'before_signup_header', '_wp_admin_bar_init' );
 add_action( 'activate_header', '_wp_admin_bar_init' );
-add_action( 'wp_footer', 'wp_admin_bar_render', 1000 );
+add_action( 'wp_body_open', 'wp_admin_bar_render', 0 );
 add_action( 'in_admin_header', 'wp_admin_bar_render', 0 );
 
 // Former admin filters that can also be hooked on the front end.

wp-includes/general-template.php

@@ -2889,6 +2889,14 @@ function wp_head() {
  * @since 1.5.1
  */
 function wp_footer() {
+	/**
+	 * Sets up the Admin Bar if the current theme does not use `wp_body_open`.
+	 *
+	 * @since 5.4.0
+	 */
+	if ( ! did_action( 'wp_body_open' ) ) {
+		add_action( 'wp_footer', 'wp_admin_bar_render', 1000 );
+	}
 	/**
 	 * Prints scripts or data before the closing body tag on the front end.
 	 *

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.4-alpha-47220';
+$wp_version = '5.4-alpha-47221';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.