RFR: 8300647: Miscellaneous hashCode improvements in java.base

[Claes Redestad]

Went through the jdk and found a few more places where `ArraysSupport::vectorizedHashCode` can be used, and a few where adhoc methods could be replaced with a plain call to `java.util.Arrays` equivalents. This patch addresses that.

After this, #12068, and #12077 I think we're reaching the limit of sensible direct use of `AS::vectorizedHashCode`. I've found a few places outside of java.base where `vectorizedHashCode` might be applicable, but none that seem important enough to warrant an export of this method outside of java.base.

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Commit messages:
 - Miscellaneous hashCode improvements in java.base

Changes: https://git.openjdk.org/jdk/pull/12093/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12093&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8300647
  Stats: 44 lines in 3 files changed: 3 ins; 33 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/12093.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12093/head:pull/12093

PR: https://git.openjdk.org/jdk/pull/12093