tabbar: fix command contributions regression (#12869)

The merge of #12799 introduced a regression in
the rendering of MenuToolbarItems that aren't
pop-up menus but instead just commands that
happen to have a menu path: they were rendered
as pop-up menus instead of simple buttons.

This fix refines the condition for the new pop-up
menu rendering to check that the menu to be
rendered is not a command to be executed
directly on click.

Fixes #12687

Signed-off-by: Christian W. Damus <cdamus.ext@eclipsesource.com>

packages/core/src/browser/shell/tab-bar-toolbar/tab-bar-toolbar.tsx

@@ -150,7 +150,7 @@ export class TabBarToolbar extends ReactWidget {
         return <React.Fragment>
             {this.renderMore()}
             {[...this.inline.values()].map(item => TabBarToolbarItem.is(item)
-                ? (MenuToolbarItem.is(item) ? this.renderMenuItem(item) : this.renderItem(item))
+                ? (MenuToolbarItem.is(item) && !item.command ? this.renderMenuItem(item) : this.renderItem(item))
                 : item.render(this.current))}
         </React.Fragment>;
     }