refactor(new_editor/app): reorganize host structure and add smoke test

new_editor/app/Features/Hierarchy/HierarchyPanelRendering.cpp

@@ -0,0 +1,60 @@
+#include "HierarchyPanelSupport.h"
+
+namespace XCEngine::UI::Editor::App {
+
+using namespace HierarchyPanelSupport;
+
+void HierarchyPanel::Append(UIDrawList& drawList) const {
+    if (!m_visible ||
+        m_treeFrame.layout.bounds.width <= 0.0f ||
+        m_treeFrame.layout.bounds.height <= 0.0f) {
+        return;
+    }
+
+    const Widgets::UIEditorTreeViewPalette palette = BuildEditorTreeViewPalette();
+    const Widgets::UIEditorTreeViewMetrics metrics = BuildEditorTreeViewMetrics();
+    AppendUIEditorTreeViewBackground(
+        drawList,
+        m_treeFrame.layout,
+        m_treeItems,
+        m_selection,
+        m_treeInteractionState.treeViewState,
+        palette,
+        metrics);
+    AppendUIEditorTreeViewForeground(
+        drawList,
+        m_treeFrame.layout,
+        m_treeItems,
+        palette,
+        metrics);
+
+    if (!m_dragState.dragging || !m_dragState.validDropTarget) {
+        return;
+    }
+
+    if (m_dragState.dropToRoot) {
+        drawList.AddRectOutline(
+            m_treeFrame.layout.bounds,
+            kDragPreviewColor,
+            1.0f,
+            0.0f);
+        return;
+    }
+
+    const std::size_t visibleIndex = FindVisibleIndexForItemId(
+        m_treeFrame.layout,
+        m_treeItems,
+        m_dragState.dropTargetItemId);
+    if (visibleIndex == UIEditorTreeViewInvalidIndex ||
+        visibleIndex >= m_treeFrame.layout.rowRects.size()) {
+        return;
+    }
+
+    drawList.AddRectOutline(
+        m_treeFrame.layout.rowRects[visibleIndex],
+        kDragPreviewColor,
+        1.0f,
+        0.0f);
+}
+
+} // namespace XCEngine::UI::Editor::App