Administration: Use wp_admin_notice() in /wp-admin/.

Add usages of `wp_admin_notice()` and `wp_get_admin_notice()` on `.notice-[type]` in the root level of `/wp-admin/`. Ongoing task to implement new function across core.

Props costdev, joedolson.
See #57791.

git-svn-id: https://develop.svn.wordpress.org/trunk@56570 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/theme-install.php

@@ -318,7 +318,15 @@ if ( $tab ) {
 	<# } #>
 
 	<# if ( data.installed ) { #>
-		<div class="notice notice-success notice-alt"><p><?php _ex( 'Installed', 'theme' ); ?></p></div>
+		<?php
+		wp_admin_notice(
+			_x( 'Installed', 'theme' ),
+			array(
+				'type'               => 'success',
+				'additional_classes' => array( 'notice-alt' ),
+			)
+		);
+		?>
 	<# } #>
 
 	<# if ( ! data.compatible_wp || ! data.compatible_php ) { #>