Handle multi-clicks in Wayland backend

[PoignardAzur]

Currently, the Wayland backend code for mouse presses is roughly this:

self.clickevent.borrow_mut().debounce(MouseEvtKind::Down(
    mouse::MouseEvent {
        pos: self.pos.get(),
        buttons: *self.buttons.borrow(),
        mods: Modifiers::empty(),
        count: 1,
        focus: false,
        button,
        wheel_delta: Vec2::ZERO,
    },
))

Notice that the click count is always one; this means double-clicks and triple-clicks aren't detected.