Menus: fixed top-level menu from not consistently using style.PopupRounding. (#4788)

+ Stack tool default size.

imgui_widgets.cpp

@@ -7050,7 +7050,9 @@ bool ImGui::BeginMenuEx(const char* label, const char* icon, bool enabled)
     if (menu_is_open)
     {
         SetNextWindowPos(popup_pos, ImGuiCond_Always); // Note: this is super misleading! The value will serve as reference for FindBestWindowPosForPopup(), not actual pos.
+        PushStyleVar(ImGuiStyleVar_ChildRounding, style.PopupRounding); // First level will use _PopupRounding, subsequent will use _ChildRounding
         menu_is_open = BeginPopupEx(id, flags); // menu_is_open can be 'false' when the popup is completely clipped (e.g. zero size display)
+        PopStyleVar();
     }
     else
     {