RFR: 8346993: C2 SuperWord: refactor to make more vector nodes available in VectorNode::make

[Emanuel Peter]

Extracted from cost-model code https://github.com/openjdk/jdk/pull/20964.

Currently, some nodes are only generated in their dedicated methods:
- VectorNode::shift_count
  - LShiftCntVNode
  - RShiftCntVNode
- VectorCastNode::make
  - Vector(U)Cast...
- VectorBlendNode has no corresponding "factory" method.

The goal is to have all available under VectorNode::make, so that they can be generated simply with the vector opcode. This is helpful for the plans with the cost-model, where the VTransform nodes will only carry the vector-opc, and I need to generate vectors for these vector-opc.

-------------

Commit messages:
 - JDK-8340093

Changes: https://git.openjdk.org/jdk/pull/22917/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22917&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8346993
  Stats: 48 lines in 2 files changed: 22 ins; 15 del; 11 mod
  Patch: https://git.openjdk.org/jdk/pull/22917.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22917/head:pull/22917

PR: https://git.openjdk.org/jdk/pull/22917