Test directory refactoring step 1.

Moving TestProjects and TestPackages under root 'TestAssets' folder.

Partial fix #1250

TestAssets/TestProjects/TestLibraryWithRunner/Test.cs

@@ -0,0 +1,12 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+
+namespace TestLibraryWithRunner
+{
+    // Need to have source code to actually publish a DLL, so please don't remove this, even though it does nothing :).
+    public class Test
+    {
+    }
+}