Another attempt to fix vertical text layout

Still the line height and depth are different, but I’m not sure id the
old behaviour was correct or not.
Add _get_glyph_name() function for HarfBuzz

Helps in debugging.
Pass FT_LOAD_NO_SCALE to FreeType functions

Getting metrics in font units (AKA unscaled) avoids hitting a number of
FreeType bugs and also matches our pre-HarfBuzz code so should be more
tested.