Function: decode-char

Decode the pair of CHARSET and CODE-POINT into a character.
Return nil if CODE-POINT is not valid in CHARSET.

CODE-POINT may be a cons (HIGHER-16-BIT-VALUE . LOWER-16-BIT-VALUE).

Optional argument RESTRICTION specifies a way to map the pair of CCS
and CODE-POINT to a character. Currently not supported and just ignored.

(fn CHARSET CODE-POINT &optional RESTRICTION)