Ceil the font height to the nearest pixel

This improves the quality and the performance of the font rendering.

src/renderer/fonts/caching_shaper.rs

@@ -203,7 +203,7 @@ impl CachingShaper {
 
  let bare_font_height = metrics.ascent + metrics.descent + metrics.leading;
  // assuming that linespace is checked on receive for validity
- let font_height = bare_font_height + self.linespace;
+ let font_height = (bare_font_height + self.linespace).ceil();
  let font_width = glyph_advance + self.options.width;
 
  (font_width, font_height).into()