[LV] Move LoopVersioning creation to LVP::execute.

At the moment LoopVersioning is only created for inner-loop
vectorization. This patch moves it to LVP::execute, which means it will
also be added for epilogue vectorization. As a consequence, the proper
noalias metadata is now also added to epilogue vector loops.

LVer will be moved to VPTransformState as follow-up.

Reviewed By: Ayal

Differential Revision: https://reviews.llvm.org/D127966