Wayland Backend file open dialogs closing prematurely

[DMJC]

In Wayland backend when an NSOpenPanel is called, the open dialog will appear briefly. Moving the cursor over the NSOpenPanel window, or any other window from the parent application causes the NSOpenPanel to immediately close. This does not close when moving the cursor over GNUstep windows from other applications. Behaviour happens on Wayfire and Ambrosia compositors.

[DTW-Thalion]

Root cause is the pointer enter/leave handlers in WaylandServer+Cursor.m building NSMouseEntered/NSMouseExited with +[NSEvent mouseEventWithType:], which raises NSInvalidArgumentException ("mouseEvent with wrong type") because those types are not in GSMouseEventMask. The raise happens in wl_display_dispatch inside -receivedEvent:. -[NSApplication run] catches and logs it, but -[NSApplication runModalSession:] runs in NSModalPanelRunLoopMode with no exception handler, so an enter or leave raised while the panel is open unwinds the modal loop and the panel closes.

#165 fixes both handlers to use +[NSEvent enterExitEventWithType:], the correct constructor. Merging it resolves this.