Prevent menu dismissal due to updates for toolbar dropdowns

When clicking a `...` dropdown menu on a toolbar, the dropdown can be dismissed if the context key changes and triggers an update to the actions for the toolbar. In notebook, we had workarounds to postpone the actions update to prevent dismissing the dropdown menu but ideally it should be handled by the toolbar itself. re * https://github.com/microsoft/vscode/commit/e7cdbd8024570a7540fcc6dc29f3ca06fd31d7df * https://github.com/microsoft/vscode/commit/c0a100d41095f506db69937a4ac8b358ada67d95