Fix frame resize flicker on macOS (bug#30699)

Fix frame resize flicker on macOS (bug#30699)

* src/nsterm.h (ns_enable_screen_updates): New function.
* src/nsterm.m (ns_enable_screen_updates):
(ns_disable_screen_updates): New functions.
(disable_screen_updates_count): Count of number of times we've called
NSDisableScreenUpdates.
(x_set_window_size): Disable screen updates when not in a live resize
loop.
* src/xdisp.c (redisplay_internal): Reenable screen updates when
redisplay doesn't complete due to a popup.
(unwind_redisplay): Reenable screen updates.