Support unscaled fonts

Created by: fschutt

Currently, you cannot get a fonts ascender / descender without scaling the font. Freetype as a FT_NO_SCALE, which just gives you the raw metrics for the font. There is a Glyph::unscaled() thing, but it doesn't help, really. The font itself has to be unscaled to get the ascender and descender correctly.

The function Font::v_metrics(&self, scale: Scale) -> VMetrics should accept a NoScale or similar as the Scale parameter.