[jdk21u-dev] RFR: 8321279: Implement hashCode() in Heap-X-Buffer.java.template

[Rui Li]

A clean backport for https://bugs.openjdk.org/browse/JDK-8321279.

This patch reduces the time to get hashcode with vectorization. In tip for over a year. Low risk. Tests are running.

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Commit messages:
 - Backport 8a0a6f8c252082050c3714d9c14ad2972ac97ecf

Changes: https://git.openjdk.org/jdk21u-dev/pull/2156/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=2156&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8321279
  Stats: 13 lines in 2 files changed: 12 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/2156.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/2156/head:pull/2156

PR: https://git.openjdk.org/jdk21u-dev/pull/2156