Use bool for booleans in font-related modules.

Use bool for booleans in font-related modules.

* font.c (font_intern_prop, font_style_to_value)
(font_style_symbolic, font_parse_xlfd, font_parse_fcname)
(generate_otf_features, font_check_otf_features, font_check_otf)
(font_match_p, font_list_entities, font_at):
* fontset.c (fontset_id_valid_p, reorder_font_vector
(fontset_find_font, Fset_fontset_font)
(face_suitable_for_char_p) [0]:
* ftfont.c (fc_initialized, ftfont_get_open_type_spec)
(ftfont_open, ftfont_text_extents, ftfont_check_otf):
(m17n_flt_initialized, ftfont_shape_by_flt):
* ftxfont.c (ftxfont_draw_bitmap, ftxfont_draw):
* nsfont.m (nsfont_draw):
* w32font.c (w32font_draw):
* w32term.c (x_draw_glyphless_glyph_string_foreground):
Use bool for booleans.
* font.h: Adjust to above API changes.
(struct font, struct font_driver, struct font_driver_list):
Use bool for booleans.
(struct font): Remove useless member encoding_type.
All users removed.
* fontset.c, xftfont.c: Omit unnecessary static decls.