Redesign redisplay interface to drop global variable updated_window.

Redesign redisplay interface to drop global variable updated_window.
Always pass currently updated window as a parameter to update routines.
* dispextern.h (updated_window): Remove declaration.
(struct redisplay_interface): Pass window parameter to
write_glyphs, insert_glyphs, clear_end_of_line, cursor_to
and after_update_window_hook.
(x_write_glyphs, x_insert_glyphs, x_clear_end_of_line, x_cursor_to):
Adjust prototypes.
* dispnew.c (updated_window): Remove.
(redraw_overlapped_rows, update_marginal_area, update_text_area)
(update_window_line): Adjust to match redisplay interface changes.
* nsterm.m (ns_update_window_begin, ns_update_window_end)
(ns_scroll_run, ns_after_update_window_line):
* w32term.c (x_update_window_begin, x_update_window_end)
(x_after_update_window_line, x_scroll_run):
* xterm.c (x_update_window_begin, x_update_window_end)
(x_after_update_window_line, x_scroll_run):
* xdisp.c (x_write_glyphs, x_insert_glyphs, x_clear_end_of_line):
Likewise.  Adjust comments where appropriate.
(x_cursor_to): Simplify because this is always called during window
update (but install debugging check anyway).
(expose_window): Check must_be_updated_p flag to see whether this
function is called during window update.