(w32_per_char_metric): Remove HDC argument. Use

(w32_per_char_metric): Remove HDC argument.  Use
cached information in emulated XFontStruct to handle common cases
quickly.  Do not allocate XCharStruct for return.
(w32_native_per_char_metric): New function.
(w32_bdf_per_char_metric): Fill in supplied XCharStruct instead of
allocating one.
(x_produce_glyphs): Don't get an HDC.  Change calls to
w32_per_char_metric to match arg change above.  Remove calls to
free results.
(w32_get_glyph_overhangs): Ditto.
(w32_cache_char_metrics): New function.