Make all NS drawing be done from drawRect

Make all NS drawing be done from drawRect

See bug#31904 and bug#32812.

* src/nsterm.m (ns_update_begin): Don't lock focus, only clip if there
is already a view focused.
(ns_update_end): Don't mess with view focusing any more.
(ns_focus): Only clip drawing if there is already a focused view,
otherwise mark area dirty for later drawing.  Renamed ns_clip_to_rect.
All callers changed.
(ns_unfocus): Don't unfocus the view any more.  Renamed
ns_reset_clipping. All callers changed.
(ns_clip_to_row): Update to match ns_clip_to_rect.
(ns_clear_frame):
(ns_clear_frame_area):
(ns_draw_fringe_bitmap):
(ns_draw_window_cursor):
(ns_draw_vertical_window_border):
(ns_draw_window_divider):
(ns_dumpglyphs_stretch):
(ns_draw_glyph_string): Only draw if ns_focus or ns_clip_to_row
return YES.
(ns_copy_bits): Remove superfluous calls to ns_(un)focus.
(ns_flush_display): New function.