Fix notebook context menu layering

Mount shadow DOM context views at the workbench container so notebook-local stacking contexts cannot obscure them behind adjacent parts.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: amunger

src/vs/platform/contextview/browser/contextViewService.ts

@@ -41,7 +41,8 @@ export class ContextViewHandler extends Disposable implements IContextViewProvid
 			domPosition = ContextViewDOMPosition.ABSOLUTE;
 		}
 
-		this.contextView.setContainer(container ?? this.layoutService.activeContainer, domPosition);
+		const contextViewContainer = shadowRoot && container ? this.layoutService.getContainer(getWindow(container)) : container ?? this.layoutService.activeContainer;
+		this.contextView.setContainer(contextViewContainer, domPosition);
 
 		this.contextView.show(delegate);