[USE_CG_TEXT_DRAWING] (mac_draw_string_cg): New function.

[USE_CG_TEXT_DRAWING] (mac_draw_string_cg): New function.
(x_draw_glyph_string_foreground) [USE_CG_TEXT_DRAWING]: Use it.
(XLoadQueryFont) [USE_CG_TEXT_DRAWING]: Set members cg_font and
cg_glyphs in struct MacFontStruct if synthesized bold or italic is
not used and font substitution never occurs for ASCII and Latin-1
characters.
(XLoadQueryFont): Maximum and minimum metrics are now those among
ASCII characters.
(XLoadQueryFont) [!MAC_OS8 || USE_ATSUI]: Apply WebKit-style
height adjustments for Courier, Helvetica, and Times.