add URLs as bad link text in link-text audit

**Feature request summary**

Please update the Links Do Not Have Descriptive Text audit to flag use of URLs as link text.

Examples of code that would be treated the same as "click here" is currently treated:
```
https://example.com/
example.com
```

**Are you willing to work on this yourself?**

Yes. That said, programming for me is a side-skill, not a primary one.

**What is the motivation or use case for changing this?**

An URL does not tell the site visitor what content they are going to get if they follow the link. It is especially meaningless to blind people who are being presented with a unified list of links on the page.

**How is this beneficial to Lighthouse?**

Lighthouse does a better job of calling out poor link text.