RFR: 8358768: [vectorapi] Make VectorOperators.SUADD an Associative

[Ian Graves]

Adding SUADD an associative operation in the Vector API. Saturated addition on fixed-width unsigned integers is provably associative.

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Commit messages:
 - Adding associative support for SUADD and associated tests

Changes: https://git.openjdk.org/jdk/pull/26099/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26099&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8358768
  Stats: 1300 lines in 35 files changed: 1299 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/26099.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26099/head:pull/26099

PR: https://git.openjdk.org/jdk/pull/26099