Improve support of specific knitr engines for source output

[cderv]

it should not be pass through so that it does not end up into the div when pass as a knitr option.

This option is new from knitr 1.38 (https://github.com/yihui/knitr/blob/master/NEWS.md#changes-in-knitr-version-138)

I don't think this option lang has any effect in Quarto yet. So we have a difference in behavior between knitr in R Markdown and in Quarto.

With knitr, lang is used in various place to change the language that will be applied as class to the code chunk in Markdown. Default is the engine. Sometimes it needs to be tweaked.

Example:

```{verbatim, lang = "js"}
console.log('test')
```

This is used in knitr to output a code chunk of class js

```{bash, lang = "default"}
pwd
```

This is used to execute a chunk as bash but highlight as a default block.

So this PR only makes sure that the option is correctly identified a knitr option. I'll make another one (or just continue in this one if you prefer) to make the recent engine (verbatim, embed, comment, ...) works correctly. They are not really working as expected I believe (mainly because we overwrite the source hook I think).

[cderv]

I added support for

```{embed, file = "special-highlight.lua"}
```

in addition of the verbatim engine.

There is still the cat engine that has a specific behavior depending on the source hook (that quarto replace). I am still onto this.

And this probably need to tests.

@yihui maybe we need to reorganize and refactor in knitr so that we could maybe not rewrite things too much and so that Quarto can directly use some knitr function.

[yihui]

@yihui maybe we need to reorganize and refactor in knitr so that we could maybe not rewrite things too much and so that Quarto can directly use some knitr function.

Sure! We should definitely do that.