Use shared assets for fonts instead of hot-linking Google Fonts

### MDN URL

https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Properties/font-stretch

### What information was incorrect, unhelpful, or incomplete?

There are 10 cases where font files are directly hot-linked from Google Fonts servers. Since these URLs are not a part of the official API, they could disappear one day:

```
https://fonts.gstatic.com/s/[…].woff2
```

### What did you expect to see?

Needed fonts added and linked from [mdn/shared-assets](https://github.com/mdn/shared-assets/)

```
/shared-assets/fonts/[…].woff2
```