Node variadic inputs to represent T as Vec<T>

[Keavon]

A node which takes a Vec should be able to expose itself as a variadic input, which looks like this:

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(7x14 rectangle with 2px rounding)

Multiple wires can enter this. The order of the wires entering the variadic input does matter, and it laid out from top to bottom. The node receives these as a Vec of T and otherwise acts normally.

The node macro can define whether a data type, that's a Vec, is shown as variadic or regular. We should also consider whether we support the Table data type, where multiple wires become multiple table rows.

[optozorax]

Since variables are currently have no names, they will only have order in this architecture.

What if I want to add new variable in the middle of the existing variables? Should I remove current last connections, add new connections, and then restore them again?

What if I have a lot of percentage values, how do I know that I connected it to the right position?

This will be much easier, if variables had names and all variables that you connect will just use name that it have.

upd: but what if I want to connect Math node to this, it has no name...

[Keavon]

Each wire simply pushes into the Vec. The node itself just receives the Vec and does what it normally does, so nothing is changed. For the "Math" node in #2459, I think we'll likely just assign A, B, C, ..., Z, AA, AB, ..., etc.

[optozorax]

That's not ergonomic for a user :( if I have a lot of variables, then I will be confused very soon by these names

[Keavon]

Let's discuss that in the issue for the Math node so we can explore some possibilities.