Type underlying value of Nodes (prototype)

[Methuselah96]

TODO:

• Bvec swizzle
• Can .x really be used on float node?
• What to do with mixed types (e.g., vec.x.addAssign(ivec4))?
• Infer node types in more cases (uniform, arrays, etc.)
• Tests?
• TextureNode can have different types
• Make sure return types are as specific as possible
• Rename TNodeValue to TNodeType
• "color" or no?
• Make sure we're not exporting more types than we want
• Move swizzle to TSLCore