(Quniscribe, QCformat): New symbols.

(Quniscribe, QCformat): New symbols.
(syms_of_w32font): Define them.
(w32font_has_char): Indicate uncertainty.
(w32font_encode_char): Encode as glyph point. Make static.
(recompute_cached_metrics): New function.
(w32font_open_internal): Use it. Set font to use glyph points
initially. Set format based on type of font.
(w32font_text_extents, w32font_draw): Optionally use glyph points.
(w32_enumfont_pattern_entity): Accept backend arg. Set type based
on it. Set format based on information available here.
(add_font_entity_to_list): Identify backend based on opentype_only.