Changing UI font

[Croworbit]

Describe the feature
Provide a clear and concise description of your feature request. Why would this feature be useful? Does the feature involve the desktop build, the web build, or both?

I just want to be able to use the default font of my OS for the UI, whatever it may be, as a non default-ruffle option on the preferences menu

I'd like to have Ruffle match my system. I also have a particular set of fonts I use for better readability, so I'd like to be able to have them
(with the font used currently stays as default until I change it)
this would be for the desktop version

[kjarosh]

Related: emilk/egui#1344