Fix display of stipples on NS with respect to cursor highlight

Fix display of stipples on NS with respect to cursor highlight

* src/nsfont.m (nsfont_draw): Delete redundant code.

* src/nsterm.m (ns_maybe_dumpglyphs_background): Conform logic
to X version by always displaying the background if s->stipple_p
should be set.
(ns_draw_stretch_glyph_string): Set stipple background as
appropriate.
(ns_set_glyph_string_gc): New function.
(ns_draw_glyph_string): Call it, as on X.  Reported by Arash
Esbati <arash@gnu.org>.