Feature request: more arguments to screenshot_pdf

[ps0ares]

Consider adding the following arguments to screenshot_pdf: print_background, pagesize and margins. That way It would be possible to print html slideshows to pdf, for example.

[Patrick330]

Please also consider scale, which could be mapped to the zoom argument already handled by webshot(). My tables print with scrollbars because I cannot scale them to match the PDF page size.

[cderv]

I believe this is also impact automatic screenshot feature for PDF in knitr when HTML content is detected (like a leaflet map). The fig.height and fig.width options of the chunk options will only have impact to set the viewport, but then the PDF output will be based on a print of the page using default pagesize (which is letter I think). This lead to wrong size screenshot on wide size webpage. (Quarto is expecting 300 DPI content which led to higher pixel size than rmarkdown).

See issue linked above for context.