Throughout the file, delete all USE_FONT_BACKEND

Throughout the file, delete all USE_FONT_BACKEND
conditionals.  Don't check enable_font_backend.  Delete all codes
used only when USE_FONT_BACKEND is not defined.
(w32font_open): Return a font-object.  Make a font-object by
font_make_object.  Adjusted for the change of struct w32font_info.
(w32font_close): Don't free struct font.  Adjusted for the change
of struct w32font_info.
(w32font_encode_char, w32font_text_extents, w32font_draw):
Adjusted for the change of struct w32font_info.
(w32font_draw): Likewise.
(w32font_list_internal): Return a list, not vector.
(w32font_open_internal): Change the 4th arg to font-object.
Adjusted for the change of struct w32font_info and font-object
format.
(add_font_name_to_list): Don't downcase names.
(w32_enumfont_pattern_entity): Make a font-entity by
font_make_entity.  Adjusted for the format change of font-entity.
Use FONT_SET_STYLE to set a style-related font property.  If a
font is scalable, set avgwidth property to 0.  Set font-entity
property by font_put_extra.
(font_matches_spec): Adjusted for the format change of
font-entity.
(w32_weight_table, w32_decode_weight): New variables.
(w32_encode_weight): New function.
(fill_in_logfont): Adjusted for the format change of font-spec.
(w32font_full_name): Use FONT_WEIGHT_SYMBOLIC to get a symbol
weight value.
(w32font_driver): Adjusted for the change of struct font_driver.

(w32font_open_internal): Change last argument from
w32font_info struct to font object.  Fill in font object from
font_entity.  Get Outline metrics if possible.  Use them to
calculate underline position and thickness.  Use xlfd name as name
property.  Don't set codepage.
(w32font_open): Pass font_object to w32font_open_internal.  Don't
update dpyinfo->smallest_font_height and
dpyinfo->smallest_char_width.
(w32font_draw): Use s->font.
(clear_cached_metrics): Don't clear non-existent blocks.