Expose public variables in subspells as input sockets on the node

[Knar]

Right now, when you use the Spell node and select a spell with Public variables exposed, you can set those public variables in the inspector window. However, you can't set these values dynamically, if for example you wanted a variable to go into a subspell. The workaround is to pack everything into the input but that's janky. It would be very nice to have the input sockets dynamically populate with the public variables available on the node.