(Qbig5, Qcn_gb, Qsjis, Qeuc_kr): Remove variables.

(Qbig5, Qcn_gb, Qsjis, Qeuc_kr): Remove variables.
(syms_of_mac): Don't initialize them.
(Vmac_charset_info_alist): New variable.
(syms_of_mac): Defvar it.
(create_text_encoding_info_alist): New function.
(decode_mac_font_name, mac_to_x_fontname)
(x_font_name_to_mac_font_name, init_font_name_table): Don't hard
code the correspondence among XLFD charsets, Mac script codes, and
Emacs coding systems.  Use Vmac_charset_info_alist and result of
create_text_encoding_info_alist instead.
(init_font_name_table) [TARGET_API_MAC_CARBON]: Use Font Manager
routines also on Mac OS Classic.
(init_font_name_table) [!TARGET_API_MAC_CARBON]: Use
add_font_name_table_entry.
(mac_do_list_fonts): Regard 0 in XLFD scaleble fields as
specified.  Derive unspecified scalable fields from specified one.
(x_list_fonts): Consider Valternate_fontname_alist.
(kDefaultFontSize): Change value from 9 to 12.
(XLoadQueryFont): Get decoded font family, font face, and charset
from x_font_name_to_mac_font_name.  Set full name of loaded font.
(mac_unload_font): Free `full_name' member.
(x_load_font): Don't try XLoadQueryFont if x_list_fonts returns
NULL.  Copy full_name member of struct MacFontStruct to that of
struct font_info.