[util] Add --font-size to hb-shape

Also makes hb-view to use 8 bits of subpixel precision and shape at
requested size, instead of always shaping at upem and scaling results.

util/hb-shape.cc

diff --git a/util/hb-shape.cc b/util/hb-shape.cc
index 01081ea..f38f387 100644
--- a/util/hb-shape.cc
+++ b/util/hb-shape.cc
@@ -126,6 +126,6 @@
 int
 main (int argc, char **argv)
 {
-  main_font_text_t<shape_consumer_t<output_buffer_t> > driver;
+  main_font_text_t<shape_consumer_t<output_buffer_t>, FONT_SIZE_UPEM, 0> driver;
   return driver.main (argc, argv);
 }