[llvm] [memprof] Add Version2 of the indexed MemProf format (PR #89100)

[Snehasish Kumar via llvm-commits]

https://github.com/snehasish commented:

Do you think we should add the v2 reader to the same patch so it can be tested as a round trip? Right now this patch doesn't have any tests.

https://github.com/llvm/llvm-project/pull/89100