[VP][DAGCombiner] Introduce generalized pattern match for vp sdnodes.

The patch tries to solve duplicated combine work for vp sdnodes. The idea is to
introduce MatchConext that verifies specific patterns and generate specific node
infromation. There is two MatchConext in DAGCombiner. EmptyMatcher is for
normal nodes and VPMatcher is for vp nodes.

The idea of this patch is come form Simon Moll's proposal [0]. I only fixed some
minor issues and added few new features in this patch.

[0]: https://github.com/sx-aurora-dev/llvm-project/commit/c38a14484aa2945f3b05369560b65916dd832f76

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D141891