P: add a "fit to screen" option as well as the existing "fill frame" option on slideshows

"Zoom to Fill Frame" crops vertical images. Sometimes I have a highly cropped image or one some one texted me as part of my collection. Manually scaling or cropping images is a lot of work for a quick slideshow. Besides, Lightroom already scales these images in the Library. This should not be a difficult option to add to the Slideshow, and would really, really improve its functionality.