Implement types and type checking in the node graph

[Keavon]

• Nodes can have generic parameters (e.g. ValueNode)
• Generics are a language abstraction and in the final binary there are actually a bunch of different implementations for value nodes (ValueNode, ValueNode)
• When stitching together nodes at runtime, we have to choose the correct concrete implementation (e.g. ValueNode)
• We currently achieve this by specifying the concrete types for everything in the ui, this is inconvenient and error prone
• Introducing type inference/checking would give immediate feedback about node graph validity (no more runtime type errors) and we could even disable runtime type checks improving performance

[Keavon]

Closed by #1025