[llvm] [memprof] Add IndexedMemProfReader::getMemProfCallerCalleePairs (PR #115807)

[Kazu Hirata via llvm-commits]

kazutakahirata wrote:

@snehasish Thank you for the feedback!  Could I address it after #116184?  The follow-up PR touches the same area.

https://github.com/llvm/llvm-project/pull/115807