[TODO] FileSystemWatcher for openDialog is not properly disposed when application shutdown

[chaojian-zhang]

Description

TODO: Currently FileSystemWatcher for openDialog is not properly disposed when application shutdown
It won't work even if we call openDialog.Dispose(); GC.Collect() also doesn't help.
See gui-cs/Terminal.Gui#1524

To test this: select some .sm2 file and choose open, then wait for a few seconds to see the exception caused due to the FileSystemWatcher still tries to call a callback that access the now null Application.Mainloop.

Screenshots

Remark

You can't force dispose all instances of a class with reflection;
Also see https://stackoverflow.com/questions/12368/how-to-dispose-a-class-in-net

Per: 2e40a21

[tznind]

I think this will be fixed by gui-cs/Terminal.Gui#1651