[llvm] [BOLT] Refactor MCInstReference and move it to Core (NFC) (PR #155846)

[Amir Ayupov via llvm-commits]

aaupov wrote:

Hi @atrosinenko,
Thank you for working on this functionality, I've experienced a similar need to track individual instructions while working on the data flow graph prototype in BOLT. 

However, using an instruction pointer can lead to hard-to-track bugs due to BB instructions reallocations (e.g. on insertion/removal) or simply deleting the instruction being referenced. Do you plan to cover that as well?

https://github.com/llvm/llvm-project/pull/155846