[llvm-exegesis] Rename InstructionInstance into InstructionBuilder. Summary: Non functional change. Subscribers: tschuett, courbet, llvm-commits Differential Revision: https://reviews.llvm.org/D50176 llvm-svn: 338701 GitOrigin-RevId: 171f3f46c869c0ec898bf4c2a33d10707fc03a9f