Synchronize joystick events between all ports

Generate wxJoystickEvent with the same fields under all platforms by
making the Linux and macOS versions follow MSW convention of using
"1 << N" for the changed button.

Add GetButtonOrdinal() accessor which can be used to retrieve just N.

Closes #18233.

include/wx/event.h

@@ -15,6 +15,7 @@
 #include "wx/cpp.h"
 #include "wx/object.h"
 #include "wx/clntdata.h"
+#include "wx/math.h"
 
 #if wxUSE_GUI
     #include "wx/gdicmn.h"
@@ -2760,6 +2761,7 @@ public:
     int GetZPosition() const { return m_zPosition; }
     int GetButtonState() const { return m_buttonState; }
     int GetButtonChange() const { return m_buttonChange; }
+    int GetButtonOrdinal() const { return wxCTZ(m_buttonChange); }
     int GetJoystick() const { return m_joyStick; }
 
     void SetJoystick(int stick) { m_joyStick = stick; }