[llvm][NFC] Replace CallSite with CallBase in Inliner

Summary:
*Almost* all uses are replaced. Left FIXMEs for the two sites that
require refactoring outside of Inliner, to scope this patch.

Subscribers: eraman, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D77817