`Application.Init` / `Shutdown` are confused about `TopLevel`s created by `Application.Begin` and not cleaned up by `Application.End`

In UI Catalog, before I start a Scenario I call Application.Shutdown. You are supposed to book end every call to Applciation.Begin with Shutdown.

I just discovered that Shutdown does not actually clean up. As a result, the next time Application.Begin is called, fields like topLevels still have data. This means that the ‘old’ stuff interferes with the ‘new’ stuff.

Short-term fix is to uninitialize stuff:

		/// <summary>
		/// Shutdown an application initalized with <see cref="Init()"/>
		/// </summary>
		public static void Shutdown ()
		{
			Driver.End ();
			foreach (var t in toplevels) {
				t.Running = false;
			}
			toplevels.Clear ();
			Current = null;
			CurrentView = null;
			Top = null;
			MainLoop = null; 
			_initialized = false;
		}

Crux of issue (added Nov 2, 2022 via #2162):

Init/Shutdown are supposed to clean up. But in ResetState, the loop that disposes of the topLevels does nothing because the Toplevel that was created by Init has not been added to topLevels (it gets added by Begin).

The right fix (IMO) would be to move all that state into RunState and leverage the fact that RunState is already IDisposable. However, it may not be possible to do this without a breaking change.

[tig]

See latest update to the PR.

I have implemented your suggested fix (with tweaks). All unit tests except KeyBindings_Command_With_MdiTop pass.

No asserts from UI Catalog.

Check it out!!!

See if you can figure out why that test broke…

[tig]

Do you think NotifyNewRunState could be invoked safely even if ExitRunLoopAfterFirstIteration is false.

ExitRunLoopAfterFirstIteration as true will exit the RunLoop and it’s needed to manually rerun it. That is only used for drivers that can’t be blocked into the RunLoop, like the WebConsole. But perhaps is safely also to invoke the NotifyNewRunState event if it’s false. I never try it but it should do not screw up anything.

I did this and wrote more unit tests to prove it works. The new docs for these actions are:

		/// <summary>
		/// Notify that a new <see cref="RunState"/> was created (<see cref="Begin(Toplevel)"/> was called). The token is created in 
		/// <see cref="Begin(Toplevel)"/> and this event will be fired before that function exits.
		/// </summary>
		/// <remarks>
		///	If <see cref="ExitRunLoopAfterFirstIteration"/> is <see langword="true"/> callers to
		///	<see cref="Begin(Toplevel)"/> must also subscribe to <see cref="NotifyStopRunState"/>
		///	and manually dispose of the <see cref="RunState"/> token when the application is done.
		/// </remarks>
		public static event Action<RunState> NotifyNewRunState;

		/// <summary>
		/// Notify that a existent <see cref="RunState"/> is stopping (<see cref="End(RunState)"/> was called).
		/// </summary>
		/// <remarks>
		///	If <see cref="ExitRunLoopAfterFirstIteration"/> is <see langword="true"/> callers to
		///	<see cref="Begin(Toplevel)"/> must also subscribe to <see cref="NotifyStopRunState"/>
		///	and manually dispose of the <see cref="RunState"/> token when the application is done.
		/// </remarks>
		public static event Action<Toplevel> NotifyStopRunState;