General: Remove noopener from links opening in a new tab.

Removes the automatic addition of `rel="noopener noreferrer"` from links targeting a new tab or window, `target='_blank'`. Since this was introduced, supported browsers have changed their security policies and no longer allow the opened link to have JavaScript access to the previous tab.

Deprecates:

* `wp_targeted_link_rel()`
* `wp_targeted_link_rel_callback()`
* `wp_init_targeted_link_rel_filters()`: converted to a noop function
* `wp_remove_targeted_link_rel_filters()`: converted to a noop function

The deprecated functions are retained in `formatting.php` as in `SHORTINIT` mode the file is included while `deprecated.php` is not.

This also removes the `noopener` from links hard coded within the WordPress dashboard linking to documentation and other resources.

Props audrasjb, azaozz, dhruval04, dorzki, neo2k23, presskopp, sabernhardt, swissspidy, tobiasbg.
Fixes #53843.

Built from https://develop.svn.wordpress.org/trunk@59120


git-svn-id: http://core.svn.wordpress.org/trunk@58516 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/includes/dashboard.php

@@ -1912,7 +1912,7 @@ function wp_dashboard_php_nag() {
 	<p class="button-container">
 		<?php
 		printf(
-			'<a class="button button-primary" href="%1$s" target="_blank" rel="noopener">%2$s<span class="screen-reader-text"> %3$s</span><span aria-hidden="true" class="dashicons dashicons-external"></span></a>',
+			'<a class="button button-primary" href="%1$s" target="_blank">%2$s<span class="screen-reader-text"> %3$s</span><span aria-hidden="true" class="dashicons dashicons-external"></span></a>',
 			esc_url( wp_get_update_php_url() ),
 			__( 'Learn more about updating PHP' ),
 			/* translators: Hidden accessibility text. */