Move char-it-table related codes to chartab.c.

Move char-it-table related codes to chartab.c.
(Vutf_2000_version): Moved to chartab.c.
(Fdefine_char): Likewise.
(Ffind_char): Likewise.
(syms_of_mule_charset): Move types `uint8-byte-table',
`uint16-byte-table', `byte-table' and `char-id-table' to chartab.c;
move functions `char_attribute_list, `find_char_attribute_table,
`char_attribute_alist, `get_char_attribute, `put_char_attribute,
`remove_char_attribute, `map_char_attribute, `define_char, `find_char,
`char_variants and `get_composite_char to chartab.c; move symbols
`=>ucs', `->decomposition', `compat', `isolated', `initial', `medial',
`final', `vertical', `noBreak', `fraction', `super', `sub', `circle',
`square', `wide', `narrow', `small' and `font' to chartab.c.
(vars_of_mule_charset): Move `utf-2000-version' to chartab.c; move
setting codes for `Vcharacter_composition_table' and
`Vcharacter_variant_table' to chartab.c.
(complex_vars_of_mule_charset): Move setting code for
`Vchar_attribute_hash_table' to chartab.c.