Consider unifying the LLVM offline cache and the AOT infrastructure

[k-ye]

We have made our first step towards the LLVM offline cache in #4500. Meanwhile, we are also developing our AOT infrastructure, tracked in #3642. There are lots of common features:

• Save/load the compiled LLVM module
• Maintain a mapping from a Taichi kernel identifier to the compiled LLVM mobile

Therefore, we should evaluate the feasibility of sharing code between these two directions.

cc @PGZXB @strongoier

[PGZXB]

Thanks & Got it! I will evaluate the feasibility of sharing code between your two directions. At the proper time, maybe when starting AOT for llvm-backend, maybe after offline-cache infra is good enough, I will refactor some offline-cache code which can be reused by AOT for llvm-backend. And merge/unify them with AOT infrastructure.