Mouse Area: add mouse wheel

[leb-kuchen]

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[leb-kuchen]

This would be useful for the sound applet, to enable changing the volume with the mouse wheel. I am not sure about the exact implementation and API. Should there be multiple functions, e.g. for vertical and horizontal scroll or a configurable duration for scrolling, considering touchpads?

[leb-kuchen]

I tested it with the example applet. It kinda works on touchpads, but works great with a mouse.

  fn view(&self) -> Element<Self::Message> {
        widget::mouse_area(
            self.core
                .applet
                .icon_button("display-symbolic")
                .on_press(Message::TogglePopup),
        )
        .on_mouse_wheel(|delta| {
            let change = match delta {
                mouse::ScrollDelta::Lines { y, .. } => y * 5.,
                mouse::ScrollDelta::Pixels { y, .. } => y.clamp(-1., 1.) * 5.,
            };
            Message::SoundChange((self.sound_percentage + change as i32).clamp(0, 100))
        })
        .into()
    }
   fn view_window(&self, _id: Id) -> Element<Self::Message> {
        let content_list = list_column().padding(5).spacing(0).add(settings::item(
            self.sound_percentage.to_string(),
            widget::slider(0..=100, self.sound_percentage, Message::SoundChange),
        ));

        self.core.applet.popup_container(content_list).into()
    }

It might be a good idea to add additional methods to the applet context, so you do not need to wrap in a mouse area. Other widgets like the slider, should be wrapped inside a mouse area and be made scroll able.