Adds a Fonts type the render interface. Here's an example of how
you could use this in `gui.zig`:
```zig
const fonts = render.Fonts.init();
defer fonts.deinit();
const count = fonts.count();
std.log.info("{} fonts", .{count});
for (0..count) |font_index| {
const name = fonts.getName(font_index);
std.log.info("font {} '{}'", .{ font_index, std.unicode.fmtUtf16Le(name.slice()) });
}
```
I tried adding Andrew's TrueType renderer as an option, however, I
realized it doesn't work with zig 0.13.0, so it'll have to wait.
Until then here's the changes needed to decouple the screen/text rendering
which would make it easier to add more text renderers and just cleans
things up a bit more in general.
