Editor: Improve no JS message for block editor.

Show the user a link to install the classic editor if they do not have JavaScript available and the plugin is not already installed.

Props bosskhj, audrasjb, huzaifaalmesbah, sajjad67, joedolson, costdev.
Fixes #59229.

git-svn-id: https://develop.svn.wordpress.org/trunk@56672 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/edit-form-blocks.php

@@ -320,20 +320,36 @@ static function ( $classes ) {
 	<div class="wrap hide-if-js block-editor-no-js">
 		<h1 class="wp-heading-inline"><?php echo esc_html( $title ); ?></h1>
 		<?php
-		$message = sprintf(
-			/* translators: %s: A link to install the Classic Editor plugin. */
-			__( 'The block editor requires JavaScript. Please enable JavaScript in your browser settings, or try the <a href="%s">Classic Editor plugin</a>.' ),
-			esc_url( wp_nonce_url( self_admin_url( 'plugin-install.php?tab=favorites&user=wordpressdotorg&save=0' ), 'save_wporg_username_' . get_current_user_id() ) )
-		);
+		if ( file_exists( WP_PLUGIN_DIR . '/classic-editor/classic-editor.php' ) ) {
+			// If Classic Editor is already installed, provide a link to activate the plugin.
+			$installed           = true;
+			$plugin_activate_url = wp_nonce_url( 'plugins.php?action=activate&amp;plugin=classic-editor/classic-editor.php', 'activate-plugin_classic-editor/classic-editor.php' );
+			$message             = sprintf(
+				/* translators: %s: Link to activate the Classic Editor plugin. */
+				__( 'The block editor requires JavaScript. Please enable JavaScript in your browser settings, or activate the <a href="%s">Classic Editor plugin</a>.' ),
+				esc_url( $plugin_activate_url )
+			);
+		} else {
+			// If Classic Editor is not installed, provide a link to install it.
+			$installed          = false;
+			$plugin_install_url = wp_nonce_url( self_admin_url( 'update.php?action=install-plugin&plugin=classic-editor' ), 'install-plugin_classic-editor' );
+			$message            = sprintf(
+				/* translators: %s: Link to install the Classic Editor plugin. */
+				__( 'The block editor requires JavaScript. Please enable JavaScript in your browser settings, or install the <a href="%s">Classic Editor plugin</a>.' ),
+				esc_url( $plugin_install_url )
+			);
+		}
 
 		/**
 		 * Filters the message displayed in the block editor interface when JavaScript is
 		 * not enabled in the browser.
 		 *
 		 * @since 5.0.3
+		 * @since 6.4.0 Added `$installed` parameter.
 		 *
-		 * @param string  $message The message being displayed.
-		 * @param WP_Post $post    The post being edited.
+		 * @param string  $message   The message being displayed.
+		 * @param WP_Post $post      The post being edited.
+		 * @param bool    $installed Whether the classic editor is installed.
 		 */
 		$message = apply_filters( 'block_editor_no_javascript_message', $message, $post );
 		wp_admin_notice(