[LV] Assert no DbgInfoIntrinsic calls are passed to widening (NFC).

When building a VPlan, BasicBlock::instructionsWithoutDebug() is used to
iterate over the instructions in a block. This means that no recipes
should be created for debug info intrinsics already and we can turn the
early exit into an assertion.

Reviewers: Ayal, gilr, rengolin, aprantl

Reviewed By: aprantl

Differential Revision: https://reviews.llvm.org/D77636