Adds support for the "Menu" socket type in for-each-element zones. This
only includes field inputs and their matching per-element values, but
not outputting attributes of type Menu (Menu attributes are not
generally supported at this point).
A dedicated enum propagation function is added for the zone input node.
This isn't technically necessary: the first 2 inputs and outputs should
be ignored but are not menus anyway. However, this is clearer and
provides a place for future changes.
Pull Request: https://projects.blender.org/blender/blender/pulls/128106
12ef319a49