* Input/IMouseDriver2.cs:
* Platform/X11/X11Mouse.cs:
* Platform/X11/XI2Mouse.cs:
* Platform/X11/Functions.cs:
* Platform/Windows/WMInput.cs:
* Platform/X11/X11GLNative.cs:
* Platform/Windows/WinRawMouse.cs: Added ability to set the position
of the mouse cursor.
[X11] Avoid grabbing the pointer, as this causes unexpected
side-effects (XInput2 stops working, debugging becomes difficult).
We now use XWarpPointer and try to discard the spurious MouseMove
events it generates.
[X11] Make cursor visible when window loses focus, to make debugging
easier. Restore previous state when it regains focus.
