Formatting: Add 'main' tag to kses

`main` is a valid HTML element that is especially valuable for KSES to support in light of full site editing.

Related: https://github.com/WordPress/gutenberg/pull/28576 for the addition of `main` to the group block.

Fixes #53156.
Props glendaviesnz.


Built from https://develop.svn.wordpress.org/trunk@50987


git-svn-id: http://core.svn.wordpress.org/trunk@50596 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/kses.php

@@ -252,6 +252,12 @@ if ( ! CUSTOM_TAGS ) {
 			'align' => true,
 			'value' => true,
 		),
+		'main'        => array(
+			'align'    => true,
+			'dir'      => true,
+			'lang'     => true,
+			'xml:lang' => true,
+		),
 		'map'        => array(
 			'name' => true,
 		),

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.8-alpha-50986';
+$wp_version = '5.8-alpha-50987';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.