KSES: Add support for `<ruby>` and related elements.

`<ruby>` element and its friends are used to attach annotation text onto a piece of text. This is especially commonly used in Japanese content, but it can also been seen in content of other languages like Chinese.

The set of elements to enable such functionality consists of `<ruby>`, `<rt>`, and `<rp>` in the [https://html.spec.whatwg.org/multipage/text-level-semantics.html#the-ruby-element HTML Standard], while some browsers (like Firefox) additionally support `<rb>` and `<rtc>` for more advanced formatting, which are not yet included in the official HTML spec, but can be found in a [https://www.w3.org/TR/html-ruby-extensions/ W3C extension].

Props upsuper, mukesh27, SergeyBiryukov.
Fixes #54698.
Built from https://develop.svn.wordpress.org/trunk@52969


git-svn-id: http://core.svn.wordpress.org/trunk@52558 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/kses.php

@@ -249,6 +249,11 @@ if ( ! CUSTOM_TAGS ) {
 		'q'          => array(
 			'cite' => true,
 		),
+		'rb'         => array(),
+		'rp'         => array(),
+		'rt'         => array(),
+		'rtc'        => array(),
+		'ruby'       => array(),
 		's'          => array(),
 		'samp'       => array(),
 		'span'       => array(

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.0-alpha-52968';
+$wp_version = '6.0-alpha-52969';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.