codefilename not shown anymore for md output

[cderv]

---
title: foo
format: commonmark
keep-md: true
---

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

This outputs with latest 1.3

# foo

``` python
import matplotlib.pyplot as plt
plt.plot([1,23,2,4])
plt.show()
```

but it outputs with latest 1.2 release

foo
================

<div class="code-with-filename">

**matplotlib.py**

``` python
import matplotlib.pyplot as plt
plt.plot([1,23,2,4])
plt.show()
```

</div>

It was lost in https://github.com/quarto-dev/quarto-cli/pull/4118/files#diff-3c9439f2bc27c905f44644b44dee252c2d2729b5da73484cbfc22e814137f98d while introducing DecoratedCodeBlock I believe.

@cscheid is it a regression on purpose ? Or could we port back the old behavior ?

Previously we did

    return pandoc.Div(
      { pandoc.Plain{pandoc.Strong{pandoc.Str(filename)}}, el:clone() },
      pandoc.Attr("", {"code-with-filename"})
    )

for non HTML format and now we just return the content of the code block

quarto-cli/src/resources/filters/customnodes/decoratedcodeblock.lua

Lines 106 to 109 in 37ce045

	else
	-- return the code block unadorned
	-- this probably could be improved
	return el

(from a discussion in #5101)

[cscheid]

It's not on purpose.

[cderv]

Ok good to know. I was going to make the PR but wasn't sure. I let you handle it then

[cscheid]

It would be great if you wanted to make the PR! The main thing is that we need DecoratedCodeBlock to handle more than just filenames (I created it to solve an HTML render ordering issue). Happy to help you if you want to make the fix.

[cscheid]

Thanks for catching this. I got confused between the listings support (which involves crossrefs) and filename support (which doesn't). I have a fix incoming.