This adds a new Render Output tab to the properties editor as discussed.
Still needs the Dimensions tab to be split, and a new icon, and maybe some other panel reshuffling (where did we decide the Audio panel would go?).
The idea is that EEVEE and Cycles viewport rendering is now what you start with, and so the first settings you need to tweak are everything that affects the look and quality of the render. Only later do you need to save the render to a file, so having Dimensions as the first open panel does not make a lot of sense anymore.
The number of panels in the render properties also got quite long and tedious too navigate, with not much space left for new features.