[VPlan] Consider all recipes in replicate blocks as sink candidates.

Update sinkScalarOperands to consider all operands of recipes in
replicate blocks as sink candidates This enables additional sinking
opportunities and is another step towards retiring LLVM IR-based
sinkScalarOperands.

This enables iterative sinking of operands for successive calls of
sinkScalarOperands.

Depends on D139788.

Reviewed By: Ayal

Differential Revision: https://reviews.llvm.org/D139790