Write proposal for simplifying/formalizing/enhancing slang's type system

[expipiplus1]

Hopefully will cover such topics as:

• How far can we write down and specify in documentation Slang's existing type system, having a set of typing judgements for Slang programs in one place would be an invaluable tool to guide type system enhancements and implementation.
• What inconsistencies or holes can we fill in our existing type system
• Is it possible and desirable to perform more type inference, and how far can it be made compatible with existing code
• Is it possible to restrain or more accurately specify tricky topics such as implicit casts and function overloading.
• What type system enhancements could we introduce with the goal of improving safety and runtime performance?

And work towards an implementation plan for some or all of these

[csyonghe]

For type system formalization, please make sure to work with @tangent-vector to see if you should collaborate on the formal spec work that she is working on: https://github.com/shader-slang/spec

[bmillsNV]

We should prioritize documenting the existing type system in the current quarter. Will likely do enhancements going forward.