Allow aborting redisplay stuck in 'parse-partial-sexp'

Allow aborting redisplay stuck in 'parse-partial-sexp'

* src/xdisp.c (display_working_on_window_p): New global variable.
(unwind_display_working_on_window): New function.
* src/keyboard.c (command_loop_1): Reset
'display_working_on_window_p' before and after executing commands.
* src/window.c (Frecenter, window_scroll, displayed_window_lines):
* src/indent.c (Fvertical_motion): Set
'display_working_on_window_p' before calling 'start_display'.
* src/syntax.c (scan_sexps_forward): Call 'update_redisplay_ticks'
after finishing the loop.