Initial use case: Kani

[celinval]

Port 1-2 Kani modules to use StableMIR APIs.

This will help us assess our APIs with a real use case.

[celinval]

We have ported most of Kani's codegen stage to use stable MIR:

• Migrate foreign function, compiler-interface and kani-middle modules to use StableMIR model-checking/kani#2959
• Migrate function, block and statement modules to StableMIR model-checking/kani#2947
• Migrate intrinsics module to use StableMIR model-checking/kani#2939
• Migrate rvalue and coercion module to use StableMIR model-checking/kani#2938
• Migrate static handling and most of the operand codegen code to StableMIR model-checking/kani#2931
• Migrate hooks and place modules to use mostly StableMIR APIs model-checking/kani#2910
• Change reachability module to use StableMIR model-checking/kani#2894
• Use stable_mir api instead of internal api for analysis model-checking/kani#2871
• Make codegen_span stable model-checking/kani#2882
• Stabilize find_debug_info model-checking/kani#2912

[celinval]

The main missing pieces are:

• Migrate code generation for types
• Migrate attribute handling
• Migrate diagnostic messages

There are a few functions that we still need to fully migrate type handling. StableMIR has no support today for attribute handling, neither emitting diagnostic messages.

[celinval]

I believe we can close this issue since we have successfully integrate Kani with StableMIR reducing more than 25% of our internal dependency with the Rust compiler. I've created other issues to track the missing infrastructure from StableMIR to allow a full migration.