Allow reversed attribute for ordered list HTML element

[lancewillett]

Update kses to allow the reversed attribute (boolean) on ol HTML elements.

Spec: ​http://www.w3.org/TR/html-markup/ol.html#ol.attrs.reversed

To test in the wp-admin editor, use markup like this:

<ol reversed="reversed">
	<li>Item 1</li>
	<li>Item 2</li>
	<li>Item 3</li>
</ol>

After publishing a new post with that HTML content, the reversed attribute should persist.

[SergeyBiryukov]

In 35960:

KSES: Allow the reversed attribute for <ol>.

Props lancewillett.
Fixes #35079.

[johnbillion]

Purely as an FYI, the reversed attribute isn't supported in any version of IE, for anything thinking of using it.