[FR] `editor.emmet.action.updateTag` fragment support

<!-- ⚠️⚠️ Do Not Delete This! feature_request_template ⚠️⚠️ --> <!-- Please read our Rules of Conduct: https://opensource.microsoft.com/codeofconduct/ --> <!-- Please search existing issues to avoid creating duplicates. --> <!-- Describe the feature you'd like. --> Currently, when using `editor.emmet.action.updateTag` to rename tags, there's no way to rename the tag to be a fragment (`<></>`). Also, when the `editor.emmet.action.updateTag` prompt shows up, hitting `enter` does the same thing as `escape` - nothing happens. Therefore, I propose a heuristic here - if the renamed tag name is empty (hit enter), rename the tag to a fragment.