Build/Test Tools: add new end-to-end tests for edge cases such as maintenance mode.

Sometimes errors only occur in unusual code paths such as the maintenance mode or installation screens. Due to lack of tests for these scenarios in core, such errors are usually only noticed very late. This change adds new end-to-end (e2e) tests to prevent regressions in the following areas:

- Maintenance mode (presence of a `.maintenance` file)
- Fatal error handler (simulated with an mu-plugin that causes an error)
- Installation screen (verifying full installation flow & that there are no database errors)

Thanks to these tests, an issue was already found and addressed in the default `wp_die` handler, as `wp_robots_noindex_embeds` and `wp_robots_noindex_search` used to cause PHP warnings due to `$wp_query` not existing.

In the future, these tests can be extended to also test scenarios like localized error pages via `wp_load_translations_early()`.

Fixes #61240.
Built from https://develop.svn.wordpress.org/trunk@58430


git-svn-id: http://core.svn.wordpress.org/trunk@57879 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/functions.php

@@ -3862,6 +3862,9 @@ function _default_wp_die_handler( $message, $title = '', $args = array() ) {
 		<?php
 		if ( function_exists( 'wp_robots' ) && function_exists( 'wp_robots_no_robots' ) && function_exists( 'add_filter' ) ) {
 			add_filter( 'wp_robots', 'wp_robots_no_robots' );
+			// Prevent warnings because of $wp_query not existing.
+			remove_filter( 'wp_robots', 'wp_robots_noindex_embeds' );
+			remove_filter( 'wp_robots', 'wp_robots_noindex_search' );
 			wp_robots();
 		}
 		?>

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.6-beta2-58429';
+$wp_version = '6.6-beta2-58430';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.