[VPlan] Add VPWidenIntOrFpInductionRecipe::isCanonical, use it (NFCI).

This patch adds VPWidenIntOrFpInductionRecipe::isCanonical to check if
an induction recipe is canonical. The code is also updated to use it
instead of isCanonicalID.

Reviewed By: Ayal

Differential Revision: https://reviews.llvm.org/D117551