Brings View disposal tests from develop (gui-cs#2948)

* Pulled Viewdisposaltests from develop

* fixed namespace

* fixed namespace

* code cleanup

UnitTests/Views/ViewDisposalTest.cs

@@ -0,0 +1,98 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reflection;
+using Terminal.Gui;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace Terminal.Gui.ViewsTests;
+public class ViewDisposalTest {
+#nullable enable
+	Dictionary<Type, object? []?> _special_params = new Dictionary<Type, object? []?> ();
+#nullable restore
+
+	readonly ITestOutputHelper _output;
+
+	public ViewDisposalTest (ITestOutputHelper output)
+	{
+		this._output = output;
+	}
+
+	[Fact]
+	[AutoInitShutdown]
+	public void TestViewsDisposeCorrectly ()
+	{
+		var reference = DoTest ();
+		for (var i = 0; i < 10 && reference.IsAlive; i++) {
+			GC.Collect ();
+			GC.WaitForPendingFinalizers ();
+		}
+#if DEBUG_IDISPOSABLE
+		if (reference.IsAlive) {
+			Assert.True (((View)reference.Target).WasDisposed);
+			Assert.Fail ($"Some Views didnt get Garbage Collected: {((View)reference.Target).Subviews}");
+		}
+#endif
+	}
+
+	void GetSpecialParams ()
+	{
+		_special_params.Clear ();
+		//special_params.Add (typeof (LineView), new object [] { Orientation.Horizontal });
+	}
+
+	WeakReference DoTest ()
+	{
+		GetSpecialParams ();
+		View Container = new View ();
+		Toplevel top = Application.Top;
+		var views = GetViews ();
+		foreach (var view in views) {
+			View instance;
+			//Create instance of view and add to container
+			if (_special_params.TryGetValue (view, out var param)) {
+				instance = (View)Activator.CreateInstance (view, param);
+			} else {
+				instance = (View)Activator.CreateInstance (view);
+			}
+
+			Assert.NotNull (instance);
+			Container.Add (instance);
+			_output.WriteLine ($"Added instance of {view}!");
+		}
+		top.Add (Container);
+		// make sure the application is doing to the views whatever its supposed to do to the views
+		for (var i = 0; i < 100; i++) {
+			Application.Refresh ();
+		}
+
+		top.Remove (Container);
+		WeakReference reference = new (Container, true);
+		Container.Dispose ();
+		return reference;
+	}
+
+	// TODO: Consoldate this with same fn that's in AllViewsTester, ScenarioTests etc...
+	/// <summary>
+	/// Get all types derived from <see cref="View"/> using reflection
+	/// </summary>
+	/// <returns></returns>
+	List<Type> GetViews ()
+	{
+		List<Type> valid = new ();
+		// Filter all types that can be instantiated, are public, arent generic,  aren't the view type itself, but derive from view
+		foreach (var type in Assembly.GetAssembly (typeof (View)).GetTypes ().Where (T => { //body of anonymous check function
+			return ((!T.IsAbstract) && T.IsPublic && T.IsClass && T.IsAssignableTo (typeof (View)) && !T.IsGenericType && !(T == typeof (View)));
+		})) //end of body of anonymous check function
+		{ //body of the foreach loop
+			_output.WriteLine ($"Found Type {type.Name}");
+			Assert.DoesNotContain (type, valid);
+			Assert.True (type.IsAssignableTo (typeof (IDisposable)));// Just to be safe
+			valid.Add (type);
+			_output.WriteLine ("	-Added!");
+		} //end body of foreach loop
+
+		return valid;
+	}
+}