[VPlan] Move DebugLoc to VPRecipeBase (NFCI).

Add a dedicated debug location to VPRecipeBase to remove another
unneeded use of the underlying LLVM IR instruction and also consolidate
various DL fields in sub classes.

Each recipe can have debug location and it shouldn't rely on reference
to the underlying LLVM IR instructions to retain it. See various recipes
that had separate DL fields already.