switch output format in vignettes to litedown html

[ben-schwen]

Follow up to #7534

Currently the translation links are only correctled rendered and displayed for the english vignettes

CI output

[ben-schwen]

I just noticed that we can test this locally with litedown::fuse('vignettes/ru/datatable-intro.Rmd') which ensures that render_translations works correctly and R CMD build . which ensure that the translation links for the english vignette are built correctly.

[aitap]

Looks like the fix in cd98747 was necessary, because when the vignette is rendered, the current directory is vignettes, not the package source root directory, so dirname(context) didn't match vignettes, at least on my PC and in CI. And the rest of the script works after the fix thanks to the dir(path) call not setting full.names = TRUE, so dirname("foo.Rmd") is still ..

The fread vignette and its translations were also using the rmarkdown syntax for inline code blocks (`r ...` instead of `{r} ...`).

So now it should be fine, right?

[ben-schwen]

When running locally I now get due to cd98747

litedown::fuse('vignettes/ru/datatable-intro.Rmd')
# Warning message:                                                   
# In normalizePath(dirname(context)) :
#   path[1]="vignettes/ru": No such file or directory

[aitap]

Thanks for noticing the issues I had missed!

[aitap]

• R CMD build ., R CMD INSTALL, browseVignettes(): links exist and point where they are supposed to
• Rscript site/render_translations.R: no more warnings, links also seem fine

I think it's ready to be merged.

[ben-schwen]

Yeah, I also just checked locally and everything looks fine. TY!