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.

samples/joytest/joytest.cpp

@@ -159,7 +159,7 @@ void MyCanvas::OnJoystickEvent(wxJoystickEvent& event)
 #if wxUSE_STATUSBAR
     wxString buf;
     if (event.ButtonDown())
-        buf.Printf("Joystick (%ld, %ld) #%i Fire!", xpos, ypos, event.GetButtonChange());
+        buf.Printf("Joystick (%ld, %ld) #%i Fire!", xpos, ypos, event.GetButtonOrdinal());
     else
         buf.Printf("Joystick (%ld, %ld)  ", xpos, ypos);