Add editor panel content host contract

tests/UI/Editor/integration/README.md

@@ -18,6 +18,7 @@ Layout:
 - `shell/editor_shell_compose/`: editor root shell compose only
 - `shell/editor_shell_interaction/`: editor root shell interaction only
 - `shell/dock_host_basic/`: DockHost interaction contract only
+- `shell/panel_content_host_basic/`: external panel body mount/switch/unmount only
 - `shell/menu_bar_basic/`: menu bar open/close/hover/dispatch only
 - `shell/context_menu_basic/`: context menu root/submenu/dismiss/dispatch only
 - `shell/panel_frame_basic/`: panel frame layout/state/hit-test only
@@ -55,6 +56,11 @@ Scenarios:
   Executable: `XCUIEditorDockHostBasicValidation.exe`
   Scope: `UpdateUIEditorDockHostInteraction(...)` basic contract only; splitter drag, tab activate/close, standalone panel activate/close, pointer capture/release request, workspace active-panel sync
 
+- `editor.shell.panel_content_host_basic`
+  Build target: `editor_ui_panel_content_host_basic_validation`
+  Executable: `XCUIEditorPanelContentHostBasicValidation.exe`
+  Scope: external HostedContent body mount/switch/unmount only; DockHost 只画 frame chrome，真实 body 由 content host 接管
+
 - `editor.shell.menu_bar_basic`
   Build target: `editor_ui_menu_bar_basic_validation`
   Executable: `XCUIEditorMenuBarBasicValidation.exe`
@@ -150,6 +156,9 @@ Selected controls:
 - `shell/dock_host_basic/`
   Drag `root-split`, click `Document A`, close `Document B`, click `Details`, close `Console`, inspect `Hover / Result / Active Panel / Visible Panels / Capture / split ratio`, press `Reset`, `Capture`, or `F12`.
 
+- `shell/panel_content_host_basic/`
+  Click `Activate Doc A / Activate Doc B / Activate Console / Close Inspector / Open Inspector`, inspect `Mounted Panels / Events` 和蓝色 external body，按 `Capture` 或 `F12`。
+
 - `shell/menu_bar_basic/`
   Click `File / Window / Layout`, move the mouse across menu items, click outside the menu or press `Esc`, press `F12`.