Create a cosmetic fix that ensures any HTML complies with the HTML5 standard wrt tag closing.

Very important is not using <div/>, <span/> or <b/>, <i/>, etc, as they will put the page into https://commons.wikimedia.org/wiki/Category:Pages_using_invalid_self-closed_HTML_tags , and could render incorrectly.

Less important is using <br> instead of <br */>, and <hr> instead of <hr/>. See T134423#2466410