[jdk17] RFR: 8266518: Refactor and expand scatter/gather tests

[Paul Sandoz]

Refactor scatter/gather tests to be included in the load/store test classes and expand to support access between `ShortVector` and and `char[]`, and access between `ByteVector` and `boolean[]`.

Vector tests pass on linux-x64 linux-aarch64 macosx-x64, and windows-x64.

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Commit messages:
 - 8266518: Refactor and expand scatter/gather tests

Changes: https://git.openjdk.java.net/jdk17/pull/48/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk17&pr=48&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8266518
  Stats: 11793 lines in 72 files changed: 6487 ins; 5271 del; 35 mod
  Patch: https://git.openjdk.java.net/jdk17/pull/48.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk17 pull/48/head:pull/48

PR: https://git.openjdk.java.net/jdk17/pull/48