Automerge: [SLP][NFC]Extract values state/operands analysis into separate class

Extract values state and operands analysis/building into a separate
class. This class allows to localize instrutions state and operands
building for future support of copyable elements vectorization.

Reviewers: HanKuanChen, RKSimon

Reviewed By: HanKuanChen

Pull Request: llvm/llvm-project#138724

Author: alexey-bataev