Rename Impl classes to follow Unity naming convention

- SelectionManagerImpl -> SelectionManager
- EditorContextImpl -> EditorContext
- Removed unused SceneManagerImpl and ISceneManager

The Impl suffix was inconsistent with Unity naming conventions.

editor/src/Application.cpp

@@ -1,6 +1,6 @@
 #include "Application.h"
 #include "Layers/EditorLayer.h"
-#include "Core/EditorContextImpl.h"
+#include "Core/EditorContext.h"
 #include "Core/EditorConsoleSink.h"
 #include <XCEngine/Debug/Logger.h>
 #include <XCEngine/Debug/FileLogSink.h>
@@ -118,7 +118,7 @@ bool Application::Initialize(HWND hwnd) {
         m_srvHeap->GetCPUDescriptorHandleForHeapStart(),
         m_srvHeap->GetGPUDescriptorHandleForHeapStart());
     
-    m_editorContext = std::make_shared<EditorContextImpl>();
+    m_editorContext = std::make_shared<EditorContext>();
     m_editorContext->SetProjectPath(exeDir);
     
     m_editorLayer = new EditorLayer();