Moved gesture tests to Avalonia.Input.

As `Gestures` is defined here, not in Avalonia.Interactivity.

tests/Avalonia.Interactivity.UnitTests/GestureTests.cs → tests/Avalonia.Input.UnitTests/GesturesTests.cs

@@ -9,7 +9,7 @@ using Xunit;
 
 namespace Avalonia.Interactivity.UnitTests
 {
-    public class GestureTests
+    public class GesturesTests
     {
         private MouseTestHelper _mouse = new MouseTestHelper();