Slides: Duplicate slide with alt-drag

Thanks for the feedback, @Peter_Green1 . We’ll pass this onto the Slides team for future consideration 🙂

I am BEGGING FOR THIS FEATURE. It’s such a common hotkey in literally all other design software (including Figma Design!!) and this has actually screwed me over several times when I’ve alt-dragged a slide, assuming it had been duplicated, and it hadn’t.