[llvm][NFC] Factor some common data in InlineAdvice

Summary:
Other derivations will all want to emit optimization remarks and, as
part of that, use debug info.

Additionally, drive-by const-ing.

Reviewers: davidxl, dblaikie

Subscribers: aprantl, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D81507