Kernel: Add support for vmmouse

We add this feature together with the VMWareBackdoor class.
VMWareBackdoor class is responsible for enabling the vmmouse, and then
controlling it from the PS2 mouse IRQ handler.

Kernel/Devices/PS2MouseDevice.h

@@ -48,6 +48,7 @@ public:
 private:
     // ^IRQHandler
     virtual void handle_irq() override;
+    void handle_vmmouse_absolute_pointer();
 
     // ^CharacterDevice
     virtual const char* class_name() const override { return "PS2MouseDevice"; }