Stub a few services, add support for generating call stacks on the CPU

Ryujinx.Core/OsHle/Services/Caps/IScreenshotService.cs

@@ -0,0 +1,20 @@
+using Ryujinx.Core.OsHle.Ipc;
+using System.Collections.Generic;
+
+namespace Ryujinx.Core.OsHle.Services.Caps
+{
+    class IScreenshotService : IpcService
+    {
+        private Dictionary<int, ServiceProcessRequest> m_Commands;
+
+        public override IReadOnlyDictionary<int, ServiceProcessRequest> Commands => m_Commands;
+
+        public IScreenshotService()
+        {
+            m_Commands = new Dictionary<int, ServiceProcessRequest>()
+            {
+                //...
+            };
+        }
+    }
+}