[Typst] Add Code Filename support

[cderv]

Discussed in #9627

^{Originally posted by MathisC22 May 9, 2024}

Description

File names of code cell blocks are not shown when using Typst as backend, whereas they do show when you use LaTeX or HTML to render the file. That is, the following cell only shows the contents:

```{.python filename="matplotlib.py"}
import matplotlib.pyplot as plt
plt.plot([1,23,2,4])
plt.show()
```

Would be really neat if it would also work with Typst!

[christopherkenny]

If helpful, I was looking for this feature and worked around it with:

#let titled-raw-block(body, filename: none) = {
  if (filename != none) {
    block(
      inset: 0em,
      fill: luma(200),
      radius: 8pt,
      outset: 0.75em,
      width: 100%,
      spacing: 2em,
      [
      #text(font: "DejaVu Sans Mono")[#filename]
      #block(
        fill: luma(230),
        inset: 0em, 
        above: 1.2em, 
        outset: 0.75em, 
        radius: (bottom-left: 8pt, bottom-right: 8pt), 
        width: 100%,
        body
      )
    ]
    )
  } else {
    body
  }
}

Code then looks like

#titled-raw-block(filename: "test.R", 
  raw(lang: "R", "test <- function() {
  x <- rnorm(100, 3, 1)
  mean(x) - 3
}
")
)

which produces

I mimicked the HTML output and then inserted this as a Typst chunk, but feel free to use this if helpful (or disregard if not).