Implement rudimentary sprite support in fake display

tests/GridOS.ConsoleTest/TestFakes/FakeDisplay.cs

@@ -1,12 +1,14 @@
 using System;
 using System.Collections.Generic;
+using System.Linq;
 using System.Text;
 
 namespace IngameScript
 {
     internal class FakeDisplay : IMyTextSurface
     {
         public event Action<string> TextWritten;
+        private List<MySprite> _spritesReceived = new List<MySprite>();
 
         public float FontSize { get; set; }
 
@@ -111,5 +113,21 @@ public Vector2 MeasureStringInPixels(StringBuilder text, string font, float scal
                 Y = fakeCharHeight // Assumes no newlines in text.
             };
         }
+
+        public MySpriteDrawFrame DrawFrame()
+        {
+            // TODO: This makes the assumption that 'draw frame' is supposed to be requested only once per frame. Would be more robust to wire some "frame start" notification into this fake class.
+            _spritesReceived.Clear();
+
+            return new MySpriteDrawFrame(
+                spriteReceiver: (sprite) => _spritesReceived.Add(sprite),
+
+                // Simply extract text from text type sprites.
+                disposeReceiver: () => TextWritten?.Invoke(
+                    string.Join(Environment.NewLine,
+                    _spritesReceived
+                        .Where(s => s.Type == SpriteType.TEXT)
+                        .Select(s => s.Data)))); 
+        }
     }
 }