KASM-1871 Add smooth scrolling

Previously all scrolling relied on "clicking" the up/down or left/right scroll buttons
which made it unprecise and to always scroll at the same speed.

Now we pass the scroll delta directly to the xorg input driver so the scroll is more responsinve and adaptive.

unix/xserver/hw/vnc/XserverDesktop.h

@@ -90,7 +90,7 @@ public:
 
   // rfb::SDesktop callbacks
   virtual void pointerEvent(const rfb::Point& pos, int buttonMask,
-                            const bool skipClick, const bool skipRelease);
+                            const bool skipClick, const bool skipRelease, int scrollX = 0, int scrollY = 0);
   virtual void keyEvent(rdr::U32 keysym, rdr::U32 keycode, bool down);
   virtual unsigned int setScreenLayout(int fb_width, int fb_height,
                                        const rfb::ScreenSet& layout);