Test directory refactoring step 1.

Moving TestProjects and TestPackages under root 'TestAssets' folder.

Partial fix #1250

TestAssets/TestProjects/TestAppWithContents/Program.cs

@@ -0,0 +1,13 @@
+using System;
+
+namespace ConsoleApplication
+{
+    public class Program
+    {
+        public static int Main(string[] args)
+        {
+            Console.WriteLine("Hello World!");
+            return 100;
+        }
+    }
+}