Add Quarto code with filename (#2776)

[Nenuial]

This is my attempt to implement code with filename in Quarto vignettes.

This would close #2776.

[jacpete]

Looks like something in this PR is throwing off the pre tags from getting the correct background color. here is the main branch rendered locally:

Vs this PR:

[Nenuial]

@jacpete Yes, you are correct. I didn't check this in dark mode, sorry about that.

It took me a while to figure out the exact elements to tweak, but I think it now works with the same colors as the base code blocks.

[jayhesselberth]

Thanks for the contribution, but I don't think this will be a heavily used feature, and it makes the link between pkgdown and quarto more tedious.

You can accomplish the same thing by including this in custom CSS in a pkgdown site.