dont render entire atlas region for font run pieces; render more minimal rasterization size

src/font_cache/font_cache.h

@@ -102,6 +102,7 @@ typedef struct F_RasterCacheInfo F_RasterCacheInfo;
 struct F_RasterCacheInfo
 {
   Rng2S16 subrect;
+  Vec2S16 raster_dim;
   S16 atlas_num;
   F32 advance;
 };