* font.c [HAVE_M17N_FLT]: Include <m17n-flt.h>.

* font.c [HAVE_M17N_FLT]: Include <m17n-flt.h>.
(font_charset_alist): Moved from xfont.c and renamed.
(font_registry_charsets): Likewise.
(font_prop_validate_otf): New function.
(font_property_table): Register it for QCotf.
(DEVICE_DELTA, adjust_anchor, REPLACEMENT_CHARACTER)
(font_drive_otf): Deleted.
(font_prepare_composition): New arg F.  Adjusted for the change of
lispy gstring.
(font_find_for_lface): New arg C.
(font_load_for_face): Adjusted for the change of
font_find_for_lface.
(Ffont_make_gstring): Adjusted for the change of lispy gstring.
(Ffont_fill_gstring): Likewise.
(Ffont_shape_text): New function.
(Fopen_font): If the font size is not given, use 12-pixel.
(Ffont_at): New arg STRING.
(syms_of_font): Initalize font_charset_alist.  Declare
Ffont_shape_text as a Lisp function.  Call syms_of_XXfont
conditionally.