Add a split button position in the navigation example

[ZhangChengLin]

https://getbootstrap.com/docs/5.3/examples/#navbars

https://getbootstrap.com/docs/5.3/components/dropdowns/#split-button

The variety of navigation bar examples provided is nice, but one form is missing, a dropdown menu with split buttons.

In addition, the drop-down menu of the split button, trigger is not a way to increase the hover.

[ZhangChengLin]

In the case of the split button, if it is in the navigation bar, the split button should be a link element, but in the current style, it cannot be seen in the navigation bar that it is a split state, and the effect of the split is not clear and the recognition is not high, especially in the form of navbars-offcanvas.