el-menu-item ，overflow ，el-tooptip, 菜单项超出隐藏，鼠标悬浮显示

在使用el-menu时，菜单文字需要做超出隐藏并且在鼠标悬浮时显示全部文字（最好是使用了el-tooptip组件），没有超出隐藏的菜单，鼠标悬浮无效果，急！！！

When using el menu, the menu text needs to be hidden and all text needs to be displayed when hovering over the mouse (preferably using the el bootip component). If there are no hidden menus, hovering over the mouse has no effect, urgent!!!

Start by reading the el-menu-item implementation and the el-tooltip component to find how menu labels and hover content are rendered. Reproduce a long label and a label that fits, then verify that only overflowing text is truncated and that hovering it shows the full text while fitting labels have no tooltip effect.

Written by the indexing model from the issue text.