[SLPVectorizer] Fix crash in vectorizeChainsInBlock for scalable vector.

The function vectorizeChainsInBlock does not support scalable vector,
because function like canReuseExtract and isCommutative in the code
path assert with scalable vectors.

This patch avoids vectorizing blocks that have extract instructions with scalable
vector..

Differential Revision: https://reviews.llvm.org/D104809