[jdk18u] RFR: 8282874: Bad performance on gather/scatter API caused by different IntSpecies of indexMap

[Tobias Hartmann]

Backport of [JDK-8282874](https://bugs.openjdk.java.net/browse/JDK-8282874). Applies cleanly. Approval is pending.

Thanks,
Tobias

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Commit messages:
 - 8282874: Bad performance on gather/scatter API caused by different IntSpecies of indexMap

Changes: https://git.openjdk.java.net/jdk18u/pull/72/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk18u&pr=72&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8282874
  Stats: 42 lines in 7 files changed: 0 ins; 0 del; 42 mod
  Patch: https://git.openjdk.java.net/jdk18u/pull/72.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk18u pull/72/head:pull/72

PR: https://git.openjdk.java.net/jdk18u/pull/72