scroll: add mouse-scroll-single-event config

[ownia]

Introduce a new config: mouse-scroll-single-event. If it is true, when mouse reporting is enabled, emit a single mouse wheel event per scroll gesture regardless of computed y.delta. This aligns other mainstream linux terminals and prevents the multiplier from inflating the number of reported events.

Fixes: #8875

	Ghostty	Alacritty	Kitty	Ghostty (mouse-scroll-single-event = true)
tmux scroll	15 lines per tick (3 * 5)	5 lines per tick	5 lines per tick	5 lines per tick
vim scroll	9 lines per tick (3 * 3)	3 lines per tick	3 lines per tick	3 lines per tick
normal scroll	3 lines per tick	1 lines per tick	5 lines per tick	3 lines per tick

tmux conf has:

set -g mouse on

vimrc has:

set mouse=a
set ttymouse=sgr

[mitchellh]

Instead of a new config, I'd rather just do the right thing here. I think we should discuss if we should always do this. cc @rockorager