Contain XCUI ImGui adapters behind explicit host seams

new_editor/src/XCUIBackend/XCUIHostedPreviewPresenter.h

@@ -260,6 +260,27 @@ public:
     }
 };
 
+class NullXCUIHostedPreviewPresenter final : public IXCUIHostedPreviewPresenter {
+public:
+    bool Present(const XCUIHostedPreviewFrame& frame) override {
+        m_lastStats = {};
+        if (frame.drawData == nullptr) {
+            return false;
+        }
+
+        m_lastStats.submittedDrawListCount = frame.drawData->GetDrawListCount();
+        m_lastStats.submittedCommandCount = frame.drawData->GetTotalCommandCount();
+        return false;
+    }
+
+    const XCUIHostedPreviewStats& GetLastStats() const override {
+        return m_lastStats;
+    }
+
+private:
+    XCUIHostedPreviewStats m_lastStats = {};
+};
+
 class QueuedNativeXCUIHostedPreviewPresenter final : public IXCUIHostedPreviewPresenter {
 public:
     QueuedNativeXCUIHostedPreviewPresenter(
@@ -306,6 +327,10 @@ inline std::unique_ptr<IXCUIHostedPreviewPresenter> CreateQueuedNativeXCUIHosted
     return std::make_unique<QueuedNativeXCUIHostedPreviewPresenter>(queue, surfaceRegistry);
 }
 
+inline std::unique_ptr<IXCUIHostedPreviewPresenter> CreateNullXCUIHostedPreviewPresenter() {
+    return std::make_unique<NullXCUIHostedPreviewPresenter>();
+}
+
 } // namespace XCUIBackend
 } // namespace Editor
 } // namespace XCEngine