[VPlan] Add predicate to VPReplicateRecipe, expand region later.

This patch adds the predicate as additional operand to VPReplicateRecipe
during initial construction. The predicated recipes are later moved into
replicate regions. This simplifies constructions and some VPlan
transformations, like fixed-order recurrence handling.

It also improves codegen in some cases (e.g. for in-loop reductions),
because the recipes remain in the same block.

Reviewed By: Ayal

Differential Revision: https://reviews.llvm.org/D143865