Support language-settings on divs in Typst

Currently, `lang` attributes on Div elements are ignored by the Typst writer:

``` markdown
::: {lang=fr}
"L'État, с'est moi!"
::: 
```

``` typst
#block[
"L'État, с'est moi!"

]
```

It might make sense to use `#set` for this, e.g.,

``` typst
#[
#set text(lang: "fr")

"L'État, с'est moi!"
]
```