UnifiedIR for Julia

Uh, hi guys. This is my PR, but you should probably know that this is an AI generated prototype based on some of my design documents, but nowhere near ready for prime time. I do want to do something like this, but whether it'll take this shape or another is still up in the air.

I guess "IR" is "intermediate representation" while "MLIR" [1] ("Multi-Level Intermediate Representation") is an IR from Chris Lattner/LLVM that is designed to be modular and extensible. For the uninitiated, I think [2] shows how the current Julia IR is generated and used in the Julia JIT compilation process

[1] https://en.wikipedia.org/wiki/MLIR_(software)

[2] https://docs.julialang.org/en/v1/devdocs/jit/

I was unaware of alternative IRs for julia (albeit I started learning much more about compilers once I left the julia ecosystem). What other IRs is this supposed to replace? And why not just go with MLIR directly?

So, does this mean faster rendering in notebooks, better debugging, fewer NVIDIA troubles?