RFR: JDK-8241030: rename HtmlTag to TagName

[Pavel Rappo]

This looks good to me.

> On 13 Mar 2020, at 21:51, Jonathan Gibbons <jonathan.gibbons at oracle.com> wrote:
> 
> Please review a mostly-trivial rename of HtmlTag to TagName, as discussed after the recent review for updating HtmlTree.
> 
> The rename was a single automated IDE operation.
> 
> In addition, some minor functionality on HtmlTag is moved to HtmlTree, which is the only place where it is used, while writing out the tree.
> 
> And, I have added additional links to pages on html.spec.whatwg.org and www.w3.org/TR/html51 to some classes in formats.html.markup. There are no manual changes to the classes in formats.html package.
> 
> One test was affected, that used the internal HtmlTag/TagName class. Apart from that, no tests were affected.
> 
> -- Jon
> 
> JBS: https://bugs.openjdk.java.net/browse/JDK-8241030
> Webrev: http://cr.openjdk.java.net/~jjg/8241030/webrev.00/index.html
>