Cleans up/Refactors View.Subviews (#3962)

* Subview clean up

* New Add/Remove event pattern

* Using Logging

* cleanup

* Subview -> SubView

* Test code cleanup. Killed many warnings.

* Fix tznind feedback

* Refactored AllViewTest helpers

* Moved keyboard tests to parallel

* Moved mouse tests to parallel

* Moved view tests to parallel

* Test code cleanup. Killed many warnings.

* dupe test

* Some mouse tests can't run in parallel because MouseGrabView

* Made SpinnerView more testable

* Moved more tests

* SubViews to IReadOnlyCollection<View>

* SubViews to IReadOnlyCollection<View> 2

* scrollbar tests

* shortcut tests

* Use InternalSubViews vs. _subviews

* Nuked View.IsAdded.
Added View.SuperViewChanged.

* API doc updats

* Unit Test tweak

* Unit Test tweak

Tests/UnitTestsParallelizable/View/Navigation/EnabledTests.cs

@@ -0,0 +1,253 @@
+using UnitTests;
+
+namespace Terminal.Gui.ViewTests;
+
+public class EnabledTests : TestsAllViews
+{
+    [Fact]
+    public void Enabled_False_Leaves ()
+    {
+        var view = new View
+        {
+            Id = "view",
+            CanFocus = true
+        };
+
+        view.SetFocus ();
+        Assert.True (view.HasFocus);
+
+        view.Enabled = false;
+        Assert.False (view.HasFocus);
+    }
+
+    [Fact]
+    public void Enabled_False_Leaves_SubView ()
+    {
+        var view = new View
+        {
+            Id = "view",
+            CanFocus = true
+        };
+
+        var subView = new View
+        {
+            Id = "subView",
+            CanFocus = true
+        };
+
+        view.Add (subView);
+
+        view.SetFocus ();
+        Assert.True (view.HasFocus);
+        Assert.True (subView.HasFocus);
+        Assert.Equal (subView, view.Focused);
+
+        view.Enabled = false;
+        Assert.False (view.HasFocus);
+        Assert.False (subView.HasFocus);
+    }
+
+    [Fact]
+    public void Enabled_False_Leaves_SubView2 ()
+    {
+        var view = new Window
+        {
+            Id = "view",
+            CanFocus = true
+        };
+
+        var subView = new View
+        {
+            Id = "subView",
+            CanFocus = true
+        };
+
+        view.Add (subView);
+
+        view.SetFocus ();
+        Assert.True (view.HasFocus);
+        Assert.True (subView.HasFocus);
+        Assert.Equal (subView, view.Focused);
+
+        view.Enabled = false;
+        Assert.False (view.HasFocus);
+        Assert.False (subView.HasFocus);
+    }
+
+    [Fact]
+    public void Enabled_False_On_SubView_Leaves_Just_SubView ()
+    {
+        var view = new View
+        {
+            Id = "view",
+            CanFocus = true
+        };
+
+        var subView = new View
+        {
+            Id = "subView",
+            CanFocus = true
+        };
+
+        view.Add (subView);
+
+        view.SetFocus ();
+        Assert.True (view.HasFocus);
+        Assert.True (subView.HasFocus);
+        Assert.Equal (subView, view.Focused);
+
+        subView.Enabled = false;
+        Assert.True (view.HasFocus);
+        Assert.False (subView.HasFocus);
+    }
+
+    [Fact]
+    public void Enabled_False_Focuses_Deepest_Focusable_SubView ()
+    {
+        var view = new View
+        {
+            Id = "view",
+            CanFocus = true
+        };
+
+        var subView = new View
+        {
+            Id = "subView",
+            CanFocus = true
+        };
+
+        var subViewSubView1 = new View
+        {
+            Id = "subViewSubView1",
+            CanFocus = false
+        };
+
+        var subViewSubView2 = new View
+        {
+            Id = "subViewSubView2",
+            CanFocus = true
+        };
+
+        var subViewSubView3 = new View
+        {
+            Id = "subViewSubView3",
+            CanFocus = true // This is the one that will be focused
+        };
+        subView.Add (subViewSubView1, subViewSubView2, subViewSubView3);
+
+        view.Add (subView);
+
+        view.SetFocus ();
+        Assert.True (subView.HasFocus);
+        Assert.Equal (subView, view.Focused);
+        Assert.Equal (subViewSubView2, subView.Focused);
+
+        subViewSubView2.Enabled = false;
+        Assert.True (subView.HasFocus);
+        Assert.Equal (subView, view.Focused);
+        Assert.Equal (subViewSubView3, subView.Focused);
+        Assert.True (subViewSubView3.HasFocus);
+    }
+
+    [Fact]
+    public void Enabled_True_SubView_Focuses_SubView ()
+    {
+        var view = new View
+        {
+            Id = "view",
+            CanFocus = true,
+            Enabled = false
+        };
+
+        var subView = new View
+        {
+            Id = "subView",
+            CanFocus = true
+        };
+
+        view.Add (subView);
+
+        view.SetFocus ();
+        Assert.False (view.HasFocus);
+        Assert.False (subView.HasFocus);
+
+        view.Enabled = true;
+        Assert.True (view.HasFocus);
+        Assert.True (subView.HasFocus);
+    }
+
+    [Fact]
+    public void Enabled_True_On_SubView_Focuses ()
+    {
+        var view = new View
+        {
+            Id = "view",
+            CanFocus = true
+        };
+
+        var subView = new View
+        {
+            Id = "subView",
+            CanFocus = true,
+            Enabled = false
+        };
+
+        view.Add (subView);
+
+        view.SetFocus ();
+        Assert.True (view.HasFocus);
+        Assert.False (subView.HasFocus);
+
+        subView.Enabled = true;
+        Assert.True (view.HasFocus);
+        Assert.True (subView.HasFocus);
+    }
+
+    [Fact]
+    public void Enabled_True_Focuses_Deepest_Focusable_SubView ()
+    {
+        var view = new View
+        {
+            Id = "view",
+            CanFocus = true
+        };
+
+        var subView = new View
+        {
+            Id = "subView",
+            CanFocus = true,
+            Enabled = false
+        };
+
+        var subViewSubView1 = new View
+        {
+            Id = "subViewSubView1",
+            CanFocus = false
+        };
+
+        var subViewSubView2 = new View
+        {
+            Id = "subViewSubView2",
+            CanFocus = true // This is the one that will be focused
+        };
+
+        var subViewSubView3 = new View
+        {
+            Id = "subViewSubView3",
+            CanFocus = true
+        };
+        subView.Add (subViewSubView1, subViewSubView2, subViewSubView3);
+
+        view.Add (subView);
+
+        view.SetFocus ();
+        Assert.False (subView.HasFocus);
+        Assert.False (subViewSubView2.HasFocus);
+
+        subView.Enabled = true;
+        Assert.True (subView.HasFocus);
+        Assert.Equal (subView, view.Focused);
+        Assert.Equal (subViewSubView2, subView.Focused);
+        Assert.True (subViewSubView2.HasFocus);
+    }
+}