GDK W32: send both smooth and discrete scrolling events

Commit 359df028 changed the code to send GDK_SCROLL_SMOOTH with deltas instead of GDK_SCROLL_(UP|DOWN|LEFT|RIGHT). Change it again, to send both the GDK_SCROLL_SMOOTH and the GDK_SCROLL_(UP|DOWN|LEFT|RIGHT) event separately, as this is what other backends (such as wayland) do.