[nfc] Factoring out utility that can be used for other object-level tools

Related rfc can be found at https://discourse.llvm.org/t/rfc-llvm-cm-cost-model-evaluation-for-object-files-machine-code/71502. We want to reuse the instruction iterator for this tool.

Reviewed By: mtrofin, kazu, jhenderson, MaskRay

Differential Revision: https://reviews.llvm.org/D152869