Node Group input control enhancements

Applicable to: all node types that allow groups General area: GUI / User interaction

Allow creation of a listbox as an input control, displaying a list of text strings to the user and routing a set value from the chosen one to the node group.

The benefits include improving clarity for the node user as to what the different options mean (instead of a "Magic number" being used as a switch), restricting inputs to a set list when a set list really are the only valid options, and generally making node groups more self-documenting.

Example Use Cases: Creation of a "Library" node of Subsurface Scattering presets. User picks from "Apple, Cream, Ketchup", outputs are one color, one radius, one IOR. User can change between Apple and Cream without rewiring the node tree. The current alternatives are either a "library" node with 3 outputs per preset, or one node for each preset. Another option would be the use of a "magic number" (1 for type 1, 2 for type 2, 3 for type 3) and dealing with the user being able to put in options like 1.2 or 2.8).

Similarly, libraries of IOR presets, lightsource color temperatures, could be reduced to one node with simple outputs, rather than one output for each option or one node for each option.

Another example where the improvement in clarity would be beneficial would be switching between generative techniques in Geometry nodes.