[TTI] NFC: Change getVectorInstrCost to return InstructionCost

This patch migrates the TTI cost interfaces to return an InstructionCost.

See this patch for the introduction of the type: https://reviews.llvm.org/D91174
See this thread for context: http://lists.llvm.org/pipermail/llvm-dev/2020-November/146408.html

Reviewed By: dmgreen

Differential Revision: https://reviews.llvm.org/D100315

GitOrigin-RevId: 1af35e77f4b8c3314dc20a10d579b52f22c75a00
20 files changed