Feature Request - Mobile Portrait Mode - specify height for menu items

[DavidGriswoldTeacher]

As small controllers such as the 8bitdo Zero and Micro have become more readily available, it is becoming more popular (though admittedly still niche) to mount the small controller at the bottom of a phone screen with suction cups, sticky pads, or an elastic band to create a Gameboy-style experience. I do this nearly every day myself.

It works very well, except when I enter the menu to adjust shaders or options I often need to remove the controller to be able to see the menu items underneath the controller.

It would be nice if I could specify a "menu area height" value in the preferences that reduces the scrollbar area to a portion of the height screen, leaving an empty space between the menu items and the bottom toolbar where one could affix a controller, as mocked up below.

This seems somewhat similar to the landscape scaling option, but perhaps even a bit easier because there is no need to worry about centering things.

I may try to tackle this myself at some point, but I have not yet configured Retroarch for compiling and do not know the best place to start - I have found the appropriate files and could probably hack something together but it is unlikely to elegant so I thought I would put the idea out there for somebody with more familiarity with the code.