Add CIRCT HW/Comb/LLHD as backend

[maerhart]

Add CIRCT as backend or replace the current Rust-LLHD backend with CIRCT. This allows us to leverage the whole CIRCT infrastructure within moore. There are, however, a few things the current backend supports that CIRCT does not.

• Link moore against CIRCTs C-API
• Generate rust bindings for the C-API using bindgen
• Write a wrapper to make creating operations, types and attributes easier and to hide unsafe code
• Add CIRCT assembly generation as in codegen.rs
• Possibly register and expose llhd-sim and other passes to the moore CLI

[fabianschuiki]

Awesome! Check out the mlir branch, I've been starting some work there.

[maerhart]

Wow what a quick response! Sorry, I haven't seen the branch before creating the issue, so I thought I'll just create a tracking issue to get an overview of what should be done. Looks really nice already!

[fabianschuiki]

#234 implements a first version of this (the old LLHD crate stuff is still there, but we can strip that out soon!).

[fabianschuiki]

Merged #234 which implements this.