ATOM-16747 RPISystemInterface::GetDefaultScene returns the scene crea… (#5153)

* ATOM-16747 RPISystemInterface::GetDefaultScene returns the scene created by PreviewRenderer but not the Main Scene
Deprecate GetDefaultScene() function.
Update all the places which use GetDefaultScene to use Scene::GetFeatureProcessorFromEntityId or GetMainScene.
Tested with Editor, UI Editor, Material Editor, game launcher.

Signed-off-by: Qing Tao <55564570+VickyAtAZ@users.noreply.github.com>

Gems/AtomLyIntegration/CommonFeatures/Code/Source/SkinnedMesh/SkinnedMeshDebugDisplay.h

@@ -48,7 +48,7 @@ namespace AZ
             // CVar for toggling the display of the scene stats
             int r_skinnedMeshDisplaySceneStats = 0;
             // SceneId to query for the stats
-            RPI::SceneId m_sceneId = RPI::SceneId::CreateNull();
+            RPI::SceneId m_sceneId;
         };
     }// namespace Render
 }// namespace AZ