Tighten XCUI hosted preview frame contract

new_editor/src/XCUIBackend/XCUIHostedPreviewPresenter.h

@@ -10,15 +10,12 @@
 #include <utility>
 #include <vector>
 
-struct ImDrawList;
-
 namespace XCEngine {
 namespace Editor {
 namespace XCUIBackend {
 
 struct XCUIHostedPreviewFrame {
     const ::XCEngine::UI::UIDrawData* drawData = nullptr;
-    ImDrawList* targetDrawList = nullptr;
     ::XCEngine::UI::UIRect canvasRect = {};
     ::XCEngine::UI::UISize logicalSize = {};
     const char* debugName = nullptr;