Refactored UI Catalog and added tons of unit tests

UnitTests/SynchronizatonContextTests.cs

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+using System;
+using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
+using System.Globalization;
+using System.Linq;
+using System.Runtime.InteropServices.ComTypes;
+using System.Threading;
+using System.Threading.Tasks;
+using Terminal.Gui;
+using Xunit;
+using Xunit.Sdk;
+
+// Alias Console to MockConsole so we don't accidentally use Console
+using Console = Terminal.Gui.FakeConsole;
+
+namespace Terminal.Gui.Core {
+	public class SyncrhonizationContextTests {
+
+		[Fact, AutoInitShutdown]
+		public void SynchronizationContext_Post ()
+		{
+			var context = SynchronizationContext.Current;
+
+			var success = false;
+			Task.Run (() => {
+				Thread.Sleep (1_000);
+
+				// non blocking
+				context.Post (
+					delegate (object o) {
+						success = true;
+
+						// then tell the application to quit
+						Application.MainLoop.Invoke (() => Application.RequestStop ());
+					}, null);
+				Assert.False (success);
+			});
+
+			// blocks here until the RequestStop is processed at the end of the test
+			Application.Run ();
+			Assert.True (success);
+		}
+
+		[Fact, AutoInitShutdown]
+		public void SynchronizationContext_Send ()
+		{
+			var context = SynchronizationContext.Current;
+
+			var success = false;
+			Task.Run (() => {
+				Thread.Sleep (1_000);
+
+				// blocking
+				context.Send (
+					delegate (object o) {
+						success = true;
+
+						// then tell the application to quit
+						Application.MainLoop.Invoke (() => Application.RequestStop ());
+					}, null);
+				Assert.True (success);
+			});
+
+			// blocks here until the RequestStop is processed at the end of the test
+			Application.Run ();
+			Assert.True (success);
+
+		}
+
+		[Fact, AutoInitShutdown]
+		public void SynchronizationContext_CreateCopy ()
+		{
+			var context = SynchronizationContext.Current;
+			Assert.NotNull (context);
+
+			var contextCopy = context.CreateCopy ();
+			Assert.NotNull (contextCopy);
+
+			Assert.NotEqual (context, contextCopy);
+		}
+
+	}
+}