Follow-up of T284883: CodeMirror – support highlighting the new <tvar> tag syntax.

Steps to replicate the issue:

Open the 2010 Wikitext Editor, CodeMirror enabled, and type the following content:

<translate>
[https://foo.foo Foo]
[<tvar name=url>https://bar.bar</tvar> Bar]
</translate>

What happens?:
Bar link URL is not highlighted as Foo link URL is.

What should have happened instead?:
cm-mw-link-ground and cm-mw-extlink-* classes should still be added to the URL.