Ability to scale performance hud

[KingVulpes]

It would be very helpful if we had the ability to scale the performance hud, I test the Steam Deck at high resolutions like 1440p or 4K for my YouTube channel and this makes the hud small and hard to see for my viewers.

[matte-schwartz]

This is a problem on handhelds that run at higher native resolutions like 1600x2560 (Legion Go) or 1920x1080 (ROG Ally) as well, but I wasn't sure what the best solution would look like and where implementation for it should come from. I tried MANGOHUD_CONFIG's font scale configuration but I wasn't able to get that working how I wanted with the SteamOS 3 overlay slider.

My Legion Go's overlay for example is quite difficult for me to read unless I'm close to the screen:

Personally I think integration with Steam display scaling settings would make the most sense here, with an override toggle to customize that further.