(XCharStruct): Remove member `valid_p'.
(STORE_XCHARSTRUCT): Don't set member `valid_p'.
(XCharStructRow): New typedef.
(XCHARSTRUCTROW_CHAR_VALID_P, XCHARSTRUCTROW_SET_CHAR_VALID): New
macros.
(struct MacFontStruct): Add member `bounds'. Remove member
`per_char'. All uses for QuichDraw Text fonts are changed to
`bounds.per_char'. ATSUI font bounds are represented as an array
`bounds.rows' of XCharStructRow's, each of which consists of a
bitmap of valid entries and an array of char bounds.