RFR: 8333840: C2 SuperWord: wrong result for MulAddS2I when inputs permuted

[Emanuel Peter]

This is an older bug, I discovered it by manual code inspection while refactoring.

I added some regression tests that produced wrong results.

You should understand the fix given the comments in the code, if not: tell me how to improve them ;)

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Commit messages:
 - move code
 - rm isa_pack_input_or_null, leave that to a refactoring
 - refactoring / simplification
 - refactor into is_muladds2i_pack_with_pack_inputs
 - fix done, need refactoring
 - more partial fix and more test
 - more tests, and beginning of fix
 - now test reproduces
 - JDK-8333840

Changes: https://git.openjdk.org/jdk/pull/19619/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19619&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8333840
  Stats: 154 lines in 3 files changed: 123 ins; 10 del; 21 mod
  Patch: https://git.openjdk.org/jdk/pull/19619.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19619/head:pull/19619

PR: https://git.openjdk.org/jdk/pull/19619