Support "/" (forward slash) in system font

The Frame doesn't show "/" so things like URLs and fractions don't show up properly. See Discord [question](https://discord.com/channels/963222352534048818/1312982229886173205). I believe the fix would be in this `system_font.h` [file](https://github.com/brilliantlabsAR/frame-codebase/blob/main/source/application/lua_libraries/graphical_assets/system_font.h)