Feature Request: Better cropping UI in Materialize Workflow

Can we have visual cropping instead of or additional to the numbers based cropping in the materialize workflow?

Justification

So, the materialize workflow is working beautifully and is kind of an underrated feature of instamat imho. But the cropping feature is kind of quintessential and right at the beginning and its just a bit clunky to control. Its just a bit difficult to set the correct scaling, so the aspect ration doesn´t get skewed and the tiny sliders in the ui to move the cropped region are also really tiny, at least on a standard fullHD laptop.

Implementation Details

Ideally we could just have an additional button in the UI that lets us define a crop region right there in the viewport of the 2d image, that we could scale and move around. That would be a lot more intuitive.
It should default to square, but an option for non-square cropping might also be interesting.
I would consider leaving the scaling of the crop purely to the sliders part of the UI, as I think its not actually needed that much: You usually wanna have ONE square, unscaled section of a foto and use that as the base, at least thats how I would do it.

Thanks @insertmesh for your feature request!