(QCf): New variable.

(QCf): New variable.
(check_gstring): Use LGSTRING_GLYPH_LEN, not LGSTRING_LENGTH.
(font_prepare_composition): Delete this function.
(font_range): Type and arguments changed.
(Ffont_make_gstring, Ffont_fill_gstring): Delete them.
(font_fill_lglyph_metrics): New function.
(Ffont_shape_text): Renamed to Ffont_shape_gstring and arguments
changed.
(syms_of_font): DEFSYM QCf.  Delete defsubr for
Sfont_make_gstring, Sfont_fill_gstring, Sfont_shape_text.  Defsubr
Sfont_shape_gstring.