Add an "Index Switch" node which is meant as a simpler version of
the "Menu Switch" from #113445 that doesn't allow naming items
or displaying them in a dropdown, but still allows choosing between
an arbitrary number of items, unlike the regular "Switch" node.
Even when the Menu Switch is included (which should be in the
same release as this), it may still be helpful to have explicit mapping
of indices, and a fair amount of the internals can be shared anyway.
Pull Request: https://projects.blender.org/blender/blender/pulls/115250
8d5aa6eed4