Problem:
With 'incsearch' enabled, the window can scroll while typing a
search pattern, but WinScrolled is not triggered until the next user
action in Normal mode. The event is effectively skipped for every
scroll that happens while the search prompt is still open.
Solution:
Call may_trigger_win_scrolled_resized() after update_screen()
in may_do_incsearch_highlighting() and finish_incsearch_highlighting().
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